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Country Life Education Seri<?s 





OF 

PLANTS 



DUGGIR 





Class 

Rook U '6 

Copyright )^° 



COPYRIGHT DEPOSrr. 



COUNTRY LIFE EDUCATION 
SERIES 



Edited by Charles William Burkett, recently Dirtctor 

of Experiment Station, Kansas State Agricultural 

College ; Editor of Atncvicaii Agr'iculturht 



TYPES, AND BREEDS OF FARM ANIMALS 
By Charles S. Flunib, Ohio State University 

I'RINCIPLES OF II REEDING 

By Eugene Davenport, University of Illinois 

FUNGOUS DISEASES OF PLANTS 

By Benjamin Minge Duggar, Cornell University 

Li press 

SOIL FERTILITY AND PERMANENT 
AGRICULTURE 

By Cyril G. Hopkins, University of Illinois 

Otiur vulinncs in preparation 



FUNGOUS DISEASES OF 
PLANTS 



WITH CHAPTERS ON 

PHYSIOLOGY, CULTURE METHODS 
AND TECHNIQUE 



BY 



BENJAiMIN MINGE DUGGAR 

PROFESSOR OF PLANT PHVSIOLOGV IN THE NEW YORK STATE 
COLLF.GE OF AGRICULTURE, CORNELL UNIVERSITY 



GINN AND COMPANY 

BOSTON • NEW YORK • CHICAGO • LONDON 



Entered at Stationers' Hall 



Copyright, igog, by 
BENJAMIN MINGE DUGGAR 



ALL RIGHTS RESERVEU 



ICI.A2r,30?4 



GINN AND COMPANY- PRO- 
PRIETORS ■ BOSTON • U.S.A. 



PREFACE 

It is a noteworthy fact that there has been available to student 
and reader no general text or reference book of American origin 
upon fungous diseases of plants. Nevertheless, for thirty years or 
more there has been active investigation in this field, and during 
much of this time instruction in plant pathology has been an 
important part of biological teaching in all colleges where plant 
industry or country-life interests have been adecjuately represented. 
In the agricultural colleges the teaching of general mycology has 
been important, and that of plant pathology is now essential. The 
presentation should be fundamental, but it should also bear a close 
relation to the affairs of life. Plant pathological work has been 
rapidly developed in all countries characterized by a progressive 
agriculture, and for European conditions the student experiences 
no great lack of reference works. 

Through the agricultural experiment stations and through the 
extension work in various states a vast amount of information with 
respect to plant diseases has been published and otherwise dissemi- 
nated, so that to every intelligent plant producer the opportunity 
has been extended of becoming more familiar with the crop rela- 
tions of destructive parasitic fungi. The student and the progres- 
sive grower require something further, and it has therefore seemed 
none too early to put in book form a comprehensive discussion of 
the chief fungous diseases of cultivated and familiar plants. It is 
not intended that this book shall be an introduction to systematic 
mycology ; yet the arrangement of the material in taxonomic se- 
quence with respect to the fungi largely eliminates the necessity 
of any mycological preparation as a prerequisite. 

As far as practicable, in the discussion of each disease, three 
important considerations have been kept in view: (i) to describe 
the pathological effects and other relations of host and parasite ; 



VI ■ prp:face 

(2) to make clear the life history of the causal fungus ; and (3) to 
indicate the approved or suggested methods of prevention or con- 
trol. The author fully recognizes that in any complete discussion 
of a fungous disease there are definite theoretical subdivisions, 
such as symptoms, pathological morphology, etiology, life cycle of 
the causal organism, etc. Nevertheless, such a system does not at 
present recommend itself. In the nomenclature of popular names 
of diseases uniformity, or special fitness, at a sacrifice of estab- 
lished usage, has been avoided. An extensive host index has been 
included in order to present in a succinct form all of the diseases 
discussed upon any host. It is, perhaps, needless to add that the 
chapters upon culture methods, technique, and physiological rela- 
tions are designed primarily for reference, and to stimulate the 
most complete use of the available material. The bibliography is 
intended to be suggestive, and the titles are made prominent that 
the suggestion may not be avoided. 

Aside from photographs and drawings made by the author, the 
illustrations have been derived from a variety of sources. Special 
acknowledgment is made to Mr. F. C. Stewart, of the New York 
Agricultural Experiment Station, and to Professors H. IT. Whetzel 
and George V. Atkinson, of Cornell University, for the privilege 
of using many negatives from their collections. Many others have 
kindly furnished material for one or more illustrations, as credited 
in the legends. In the preparation of the drawings much assistance 
has been given by Mrs. B. M. Duggar. For helpful suggestions 
respecting the manuscript and for a first draft of the synopsis of 
species among the Uredinales, the writer is indebted to Professor 
George P. I. Reed, of the University of Missouri. 

li. M. DUGGAR 



CONTENTS 

Page 

Introduction i 

PART I. CULTURE METHODS AND TECHNIQUE 

Chai'tkk 

I. Isolation and Pure-Culture Methods 9 

I. The Development and Application of Culture Methods lo 

II. Cleaning Glassware '2 

III. The Principles and Methods of Sterilization 15 

IV. Preparation of Culture Media 23 

Liquid Media 23 

Solid Media 26 

Neutralization of Culture Media 33 

V. Present Method of isolating Organisms 34 

II. Technique of Fl\in(;, Imbeddinc;, and Staining' ... 41 

I. Fixing 4' 

II. The Paraffin Process : Infiltration and Imbedding ... 45 

HI. Staining 4^^ 

PART II. PHYSIOLOGICAL RELATIONS 

HI. Germination Studies 55 

IV. General Relations to Environmental Factors ... 62 

1. Saprophytism and Parasitism 62 

II. General Relations to Climatological Factors 66 

HI. Special Relations to Environmental Factors 69 

V. Artificial Infection 76 

VI. The Principles of Disease Control 85 

I. Methods of Control 85 

II. Preparation of Fungicides 88 

PART in. FUNCIOUS DISEASES OF PLANTS 

VII. General Classification 93 

I. Fungous Diseases and Pathology 93 

II. The Classes of Fungi 94 

VIII. Mvxomvcetes. Slime Molds 97 

I. Phytomyxales (Phytomyxaceae) 97 

II. Club Root of Cabbage and Other Crucifers 97 



viii ■ CONTENTS 

Chapter Page 

IX. SCHIZOMYCETES. BACTERIA , . I03 

I. Bacteriaceae 106 

II. Black Rot of Cabbage 107 

III. Wilt of Sweet Corn iii 

IV. Crown Gall of Apple, Peach, and Other Plants . . . 114 
V. Olive Knot, or Tubercle-Disease of the Olive . . . . 118 

VI. Bean Blight 119 

VII. Hyacinth Disease 120 

VIII. Bundle Blight of Sugar Cane 120 

IX. Pseudomonas : Other Species 120 

X. Pear Blight 121 

XI. Wilt of Cucurbits 129 

XII. Soft Rot of Carrot and Other Vegetables 131 

XIII. Soft Rot of the Calla 133 

XIV. Wilt of Solanaceae ...'.... 134 

XV. Bacillus : Other Species 1 34 

X. Phycomycetes 135 

I. Chytridiales 136 

II. Synchytriacese 136 

III. Cranberry Gall 138 

ly. Pycnochytrium Globosum (Schroet.) Schroet 139 

V. Chytridiales: Other Species 139 

VI. Saprolegniales 140 

VII. A Damping-off Fungus 141 

VIII. Brown Rot of the Lemon 144 

IX. Peronosporales 147 

X. White " Rust " of Crucifers 149 

XI. Cystopus : Other Species 152 

XII. Downy Mildew of the Grape 152 

XIII. Downy Mildew of the Cucumber 158 

XIV. Sclerospora 161 

XV. Downy Mildew of Crucifers 161 

XVI. Onion Mildew 162 

XVII. Peronospora : Other Species 164 

XVIII. Downy Mildew of the Lettuce 164 

XIX. The Late Blight and Rot of the Potato 165 

XX. Downy Mildew of Lima Beans 171 

XI. ASCOMYCETES 174 

I. Exoascaceas i75 

II. Peach Leaf Curl 176 

III. Plum Pockets 183 

IV. Witches' Broom of the Cherry 185 

V. Helotiaceae 185 

VI. Sclerotinia 186 



CONTENTS ix 

Chapter Pagf. 

XI. AscoMVCETES {Cotitinued) 

VII. Brown Rot of Stone Fruits 187 

VIII. Gray Mold, or Botrytis Disease 196 

IX. Lettuce Drop 198 

X. Stem Rot of Clover 201 

XI. Larch Canker 202 

XII. Mollisiaceae 203 

XIII. Alfalfa Leaf Spot 203 

XIV. Anthracnose of Currants . : 204 

XV. Phacidiaceae 207 

XVI. The Black Spot of Maple 208 

XVII. Perisporiales 209 

XVIII. Perisporiaceas 209 

XIX. Root Rot of Tobacco, Violets, Peas, Lupines, etc. . 210 

XX. Sooty Mold of Orange 213 

XXI. Erysiphaceas 215 

XXII. The Gooseberry Mildew 221 

XXIII. Mildew of Peach. Rose Mildew 224 

XXIV. Mildew of Apple and Cherry . . 226 

XXV. Powdery Mildew of Peas 227 

XXVI. Mildew of Composites and Other Plants .... 228 

XXVII. Mildew of Woody Plants 228 

XXVIII. Powdery Mildew of (irape 229 

XXIX. Powdery Mildew cf Willow and Poplar .... 230 

XXX. Common Mildew of Trees 23 1 

XXXI. Hypocreaceae 232 

XXXII. Wilt Disease of Cotton, Cowpea, and Watermelon . 233 

XXXIII. A Canker of Woody Plants 239 

XXXIV. European Apple Canker 242 

XXXV. Stem Rot of Sweet Potato and Eggplant .... 243 

XXXVI. Ergot 244 

XXXVII. Dothidiace^ 248 

XXXVIII. Black Knot of Plums and Cherries 248 

XXXIX. SphjEriales 253 

XL. Black Rot of Grapes 254 

XLI. Cranberry Scald 259 

XLII. Leaf Spot of Strawberry , 261 

XLIII. Leaf-Spitting Blight of Sugar Cane 263 

XLIV. Apple Scab and Pear Scab 264 

XLV. Bitter Rot of the Apple and Other Fruits . . . . 271 

XLVI. Anthracnose of Sycamore 278 

XLVII. A Disease of Young Oaks 280 

XLVIII. Bark Disease of Chestnut 281 

XLIX. Blister Canker of Apple 282 



X CONTENTS 

Chaftf.r Page 

XII. FuNCii Imperfect! 285 

I. Hyphomycetes 286 

II. Melanconiales 288 

III. Sphasropsidalcs 289 

IV. Potato Scab 290 

V. Bud Rot of Carnations 293 

VI. A Pink Rot following Apple Scab 295 

VII. Ramularia 296 

VIII. Cercosporella 297 

IX. Rice Blast 297 

X. Polythrincium 298 

XI. Peach and Apricot Scab 299 

XII. Cladosporium : Other Species 300 

XIII. Early Blight of the Potato 301 

XIV. Onion Mold 304 

XV. Macrosporium : Other Species 304 

XVI. Blight of Ginseng 305 

XVII. Leaf Spot of Beets 309 

XVIII. Early Blight of Celery 312 

XIX. Leaf Blight of Cotton 313 

XX. Cercospora : Other Species 314 

XXI. Spongy Dry Rot Fungus of Apple 316 

XXII. Dry Rot of Potatoes 317 

XXIII. Flax Wilt 319 

XXIV. Fusarium : Other Species 320 

XXV. Root Rot of the Vine 321 

XXVI. Anthracnose of Bean 322 

XXVII. Anthracnose of Cotton 325 

XXVIII. Wither-Tip and Spot of Citrus Fruits .... 327 

XXIX. Anthracnose of Clover and Alfalfa 328 

XXX. Anthracnose of Snapdragon 329 

XXXI. Colletotrichum : Other Species 330 

XXXII. Gloeosporium 330 

XXXIII. Anthracnose of Grape 332 

XXXIV. Anthracnose of Raspberry and Blackberry . . . 334 
XXXV. Gloeosporium: Other Species 335 

XXXVI. Marsonia 336 

XXXVII. Peach Blight 336 

XXXVIII. Leaf Blight of Cranberry 338 

XXXIX. Shot-Hole Disease of Plum and Cherry .... 339 

XL. Fruit Spot of Apple 341 

XLI. Heart Rot and Blight of Beets 343 

XLII. Dry Rot of Sweet Potato 344 

XLIII. Seedling Stem Blight of Eggplant 345 



CON'l'KN'rS xi 

Chai'trk Page 

XII. Fux(;i Imi'ekfecti {Coiitiiiucd) 

XLIV. I'hyllosticta 345 

XLV. Black Rot of Sweet Potato 348 

XLVl. Black Rot and Canker of Pomaceous Fruits . . . 350 

XLVII. Raspberry Cane Blight 354 

XLVIII. Rose Leaf Blotch 357 

XLIX. Leaf Spot of the Pear 358 

L. Late Blight of Celery 361 

LI. Septoria : Other Species 362 

LI I. Currant Cane Blight 364 

LI 1 1. Leaf Blight of Pear and Quince 365 

LIV. Sooty Blotch and Fly Speck of the Apple and Other 

Plants 367 

XIII. Hemihasidiomvcetes 370 

I. Ustilaginales 370 

II. Loose Smut of Oats 372 

III. Loose Smut of Wheat . . . 375 

IV. Smut of Corn 376 

V. Smut of Blue-Stem Grass 378 

VI. Tolyposporium bullatum (Schroet.) Schroet. '. . . 378 

VII. Bunt, or Stinking Smut of Wheat 379 

VIII. Tilletia : Other Species 380 

IX. Entyloma 380 

X. Onion Smut 381 

XIV. Protobasidiomycetes 384 

I. Rust Fungi 384 

II. Families and Genera 388 

III. Synopsis of Species 391 

IV. Clover Rust 395 

V. Rust of Beans 397 

VI. Rust of Vetch and Garden Pea 398 

VII. Beet Rust 399 

VIII. Carnation Rust 399 

IX. LIromyces : Other Species 402 

X. Asparagus Rust 403 

XI. Violet Rust 407 

XII. Mint Rust 407 

XIII. Black Rust of Grain 408 

XIV. Rust of Maize 414 

XV. Timothy Rust 415 

XVI. Brown Rust of Wheat and Rye 416 

XVII. Rust of Stone Fruits 417 

XVIII. Hollyhock Rust 419 



xil CONTENTS 

Chafter Page 

XIV. PROTOBASiDiOiMYCETES {Continued) 

XIX. Puccinia : Other Species 420 

XX. Gymnosporangium 422 

XXI. Cedar Apples and Apple Rust 425 

XXII. Gymnosporangium: Other Species 426 

XXIII. Orange Rust of Raspberry and Blackberry . . . 427 

XXIV. Rust of Roses 430 

XXV. Rust of Rhododendron and Norway Spruce . . . 432 

XXVI. The European Currant Rust 433 

XXVII. Orange Rust of Aster and Golden-rod 435 

XXVIII. Rust of Poplar 437 

XV. AUTOBASIDIOMYCETES 439 

I. Exobasidiales 439 

II. Gall of Heaths 440 

III. Hymenomycetales 441 

IV. A Root and Stem Rot Fungus 444 

V. Heart Rot of Sugar Maple 452 

VI. White Rot of Deciduous Trees 453 

VII. Decay, or Brown Rot, of Trees 457 

VIII. Polyporus : Other Species 462 

IX. Fomes 464 

X. A Brown Rot of Conifers 467 

XI. Root Disease of Sugar Cane 469 

XII. Root Rot of Fruit Trees 471 

XIII. The Honey Agaric 473 

XIV. European Root Disease of Alfalfa and Other Plants 477 
XV. Root Rot of Cotton and Alfalfa 479 

Host Index 483 

General Index 499 




Downy Mildew on Niagara Grapes 



FUNGOUS DISEASES OF 
PLANTS 



INTRODUCTION 

A proper study of the funij^ous diseases of plants is at once sci- 
entific and practical. The fungi were carefully studied, however, 
long before their importance as disease-producing organisms was 
recognized. A history of our knowledge of the fungi in general, 
therefore, takes us through periods when the scientific and the 
practical attitudes were not associated ; yet a brief historical survey 
must develop important and interesting facts bearing upon the 
relations of scientific work to practical affairs. 

Systematic mycology. A careful study of the fungi as independ- 
ent groups of plants was begim in the latter part of the eighteenth 
century, and if we examine the results of the work beginning at 
that time and continuing into the early half of the nineteenth cen- 
tury, it will be found that this period was one of most accurate 
and painstaking endeavor in systematic mycology. Much credit is 
therefore due to the more prominent students of that time, such 
as Bulliard, Persoon, Nees von Esenbeck, Schweinitz, Leveille, 
Fries, and Berkeley. The work so well begim was continued into 
the second half of the same century, and among the names particu- 
larly associated with that period are those of Fuckel, Karsten, the 
Tulasne brothers, Corda, and many others. This systematic study 
has, of course, continued to the present time, although the nature of 
the work produced has undergone important changes. Two phases 
in the modern development of this systematic work are well shown 
by the appearance, on the one hand, of Saccardo's monumental 
" Sylloge," and, on the other hand, of such complete morphological 
monographs as Thaxter's " Laboulbeniaceae." 



2 FUNGOUS DISEASES OF PLANTS 

Physiology and morphology. The progress in systematic my- 
cology has made possible for more than half a century a compre- 
hensive study of the diseases of plants ; yet systematic study alone 
is. not responsible for the rapid progress subsequently achieved in 
plant pathology. A number of causes might be suggested as of 
importance in the development of the latter field. It should not 
be overlooked that advances in general plant physiology were also 
manifest at about the beginning of the nineteenth century, and 
that this phase of botany had undergone unusual development 
toward the middle of the century, under the influence of Sachs 
and other experimentalists of his time. Again, a more intensive 
method in the study of morphology had been introduced, and in 
mycology the efforts of such men as the Tulasne brothers had 
shown what could be done in carefully following out the life his- 
tories or development of the fungi. Beginning about the middle 
of the nineteenth century, another distinctive epoch is entered 
upon, and the developments of this period are due chiefly to Anton 
de Bary and his contemporaries. 

The rise of plant pathology. De Bary became the conspicuous 
leader in this field, establishing in an incontrovertible manner the 
connection between the polymorphic stages of certain parasitic 
species, and the possibility of following, under well-controlled con- 
ditions, the development of little-known groups. His work was, 
furthermore, particularly significant in that he so thoroughly appre- 
ciated the nature of parasitism, the epidemic character of fungous 
diseases of plants, and the practical value of methods of inoculation 
and infection. To him more than to any one else we owe the influ- 
ence which directed future work along the lines of the most profit- 
able research. This period witnessed also the advances made by 
Pasteur and others in the study of fermentation and disease, and 
it wa^ closely followed by those perfections in the development of 
pure culture methods which have finally resulted in the possibility 
of cultivating practically all bacteria and a very great majority of 
the fungi. In the study of the fungi as the cause of plant diseases, 
at this time, valuable service was also done by Kiihn, who in his 
early career devoted himself particularly to a study of the fungous 
parasites of cultivated plants. The last decades of the century yield 
work of such diversity and importance that it is impossible here to 



INTRODUCTION 3 

do more than make briefest reference to it. The work of Brefeld 
is perhaps most distinctive, and while his theoretical views have 
not had a host of followers, his fundamental studies in the general 
field of mycology, and particularly, in this connection, his wide 
range of experiments in the artificial cultivation of organisms, are 
invaluable. Among many others who contributed special service in 
some phase of pathological or general mycological work of that 
time may be mentioned also Frank, Hartig, Schroeter, Sorauer, and 
Winter in Germany; Oudemans in Holland ; Cornu, Millardet, and 
Prillieux in France ; Comes in Italy ; Woronin in Russia ; Eriksson 
in Scandinavia ; Plowright and Ward in England ; Farlow, Burrill, 
and many others in the United States. The work has continued 
vigorously, investigations and problems have multiplied, and with 
adequate conservatism the outlook is most encouraging. 

There were some indications of a plant pathology in existence 
from the time of the first studies in systematic mycology, but an 
examination of the books which purport to be discussions of plant 
pathology shows that they were in large part an attempt to classify 
and suggest ideas having to do with plant diseases, after the man- 
ner of the older attempts which were made in human medicine. In 
most cases the life history of the organism which caused the disease 
was entirely unknown ; and, in fact, there is no plant pathology 
which deserves the name affixed to it prior to the appearance of 
Kiihn's "Die Krankheiten der Kulturgewachse, " Berlin, 1858, 
Between that time and 1900 an extensive literature developed. 
The status of the morphological work is well shown by De Bary's 
" Morphologic und Biologic der Pilze," etc., and in addition to many 
special life-history or monographic studies we have, from the patho- 
logical point of view, such comprehensive reference books as those of 
Comes, Frank, Hartig, Prillieux, Sorauer, Tubeuf, Ward, and others. 

Practical pathology and disease control. An important epoch 
in the general study of fungous diseases had its beginning in the 
prevalence of grape diseases in France, which condition led to the 
discovery of Bordeaux mixture by Millardet in France about 1883. 
After the severe tests to which the copper mixtures were subjected, 
it became evident that there was a bright prospect for controlling 
many of the fungous diseases of plants, and there developed therefore 
an immediate need for plant pathologists, or students of fungous 



4 FUNGOUS DISEASES OF TLANl'S 

diseases of plants, — persons- who should be, at the same time, 
appreciative of the problems of disease control. Incidentally it may 
be noted that plant diseases were, for the most part, understood 
to be of fungous origin. In the United States this was more or less 
coincident with the organization of a section of Plant Pathology in 
what was then the Division of Botany at Washington, and with the 
development of plant pathological work in many of the state ex- 
periment stations. In a very short time there was unusual activity 
in this study throughout the country. There was also much stimulus 
to the further development of the work in Europe, and the outcome 
was that the foundations were laid for a more careful study of the 
fungi from a phytopathological point of view. In this country the 
work was directed more especially toward immediately practical 
ends, and that which was accomplished within a brief period of time 
through the efforts initiated by Scribner and Galloway was remark- 
able. In more recent times the work has also been put upon a 
higher plane, and investigations along broader and more funda- 
mental lines have gone forward rapidly at many points throughout 
the country, so that to-day the extent of the organization and equip- 
ment for research in this field is better than may be found anywhere 
else in the world. It is perhaps fortunate that this work in the 
United States has developed in conjunction with the agricultural 
experiment stations, although, when the equipment in men, books, 
and apparatus was new, many mistakes were made. This associa- 
tion of the work insures that the direction of it will be at least 
more practical than if confined more or less to investigations carried 
on in botanical gardens or herbaria. It is perhaps to be regretted 
that there cannot be more unity of action, or cooperation, in the 
study and control of epidemic diseases. This, however, may be 
brought about in the course of time. 

Some aspects of modern plant pathology. It is very evident from 
the nature of the study, as well as from the historical notes which 
have been presented, that an analysis of the modern work in plant 
diseases indicates several important aspects, which may be grouped 
in the following category : (i) mycological relations ; (2) anatomical 
effects ; (3) physiological relations ; (4) control measures. 

Mycological relations. The mycological aspect will be concerned 
more particularly with a minute investigation of the fungi from 



IN'I'RODUCTION 5 

systematic, morphological, and physioloi^ical standpoints. Too often, 
in the early work, the chief object of the study has been to identify 
the fungus associated with a given disease and to describe its fruit- 
ing stages. An investigation of the fungus, however, should include 
an account of its complete life history wherever possible, the rela- 
tions of the fungus to conditions under which it is injurious, the 
character of the growth ]3roduced upon various culture media (when 
the organism is culturable), the conditions under which fruiting 
stages may be developed, etc. In the course of time, therefore, it 
will be necessary to repeat much of the work of earlier date, which 
has seemed to be more or less complete. 

Anatomical effects. The anatomical study, in the sen^e in which 
it is here used, will be concerned with the relations of the host to 
the parasite, in so far as the former may be modified in growth or 
minute structure. All lesions, hypertrophies, or other structural 
changes produced in the host plant are worthy of the closest atten- 
tion. These changes in the host are most diverse, varying, on the 
one hand, from minute modifications of a single cell, or of a small 
group of cells, to those changes of form which involve an immense 
increase in the size of the host organism, often giving rise to rela- 
tively enormous deformities, such as may be noted in the case of 
the club root of cabbage, plum pockets, cankers, and smut of corn. 
Again, the deformities may result in the pushing into growth of an 
abnormal number of buds, in many instances accompanied by de- 
creased size of the branches and changes in the trophic relations, 
such as to develop the various forms of witches' brooms. The 
anatomical changes^ in the host are those most commonly termed 
pathological changes. Unfortunately these are often discussed as 
if they were the only pathological effects. They are, at any rate, 
the chief evident pathological effects in many cases, and for that 
reason they constitute in fhe popular view that which is properly 
designated " plant pathology." 

Physiological relations. In close connection with the anatom- 
ical changes produced in the host, a study should be made of the 
physiological relations of host and parasite, particularly of the 

^ Kuster (Pathologische Pflanzenanatomie, 312 pp., 121 figs., 1903) has at- 
tempted a general classification of anatomical modifications induced by diverse 
stimuli. 



6 FUNGOUS DISEASES OF PLANTS 

physiological disturbances in the host itself .^ The normal physiology 
of th^ host requires attention in order that a proper comparative study 
may be made. The conditions which predispose the host plant to 
attack, or, in other words, the conditions favorable to the penetration 
of the fungus and its development within the host are most funda- 
mental from the standpoint of pathology, and also in order that 
control measures may be properly developed. It is a direction in 
which future work promises most profitable returns. Very little of 
lasting value has been done towards determining the exact condi- 
tions under which the host plant is most susceptible to attack. It 
is well known in the case of certain forced plants that the undue 
suffusion of the plant with water, whether due to lack of ventilation 
or to a combination of causes, is a certain factor in inducing disease. 
Under such conditions many fungi are able to gain entrance and 
become the cause of epidemics, whereas, under more normal con- 
ditions, they may remain as harmless inhabitants of dead materials. 

Every season shows differences in the prevalence of the more 
injurious fungous diseases. One season the brown rot of the peach 
may affect only extremely sensitive varieties, and the following 
season it may cause the loss of those most resistant. Again, some 
varieties of the host may be, under most conditions, but slightly 
predisposed to attack, notable instances being those of the very 
slight predisposition of the Kieffer pear to the blight, or in the 
resistance of certain American varieties of grapes to the downy 
mildew. Such cases might be multiplied indefinitely, and, in fact, 
there is scarcely a known fungous disease of the variable cultivated 
crops with reference to which all varieties of the host plant are 
equally susceptible. This important fact has led to the selection 
and to the production through hybridization of varieties which shall 
at once possess both the qualities desired from the standpoint of 
their own fruits or other products, and which shall, at the same 
time, carry with them the high resistance necessary to enable them 
to compete with the fungous pests. 

The effect of the fungus upon the host may be, further, merely 
to modify the quality of the product, such as the sugar or starch 
content, without seriously affecting the appearance of the economic 
product. In fact, the different means whereby the effect of the 

1 See Ward, H. M., Disease in Plants, 1901. 



INTRODUCTION 7 

fungus may show itself in slight physiological disturbances of the 
host are too numerous for special consideration. 

Control measures. Control measures for the prevention of fun- 
gous diseases should be a part of every study which is undertaken. 
Reference has already been made to the very rapid development 
of systematic methods of control. Control may be developed along 
one or more very different lines. In the first place, it may concern 
itself more particularly with a maintenance of the host plant in a 
thoroughly sanitary environment, or in one which renders it more 
resistant to the attacks of fungi. It may again concern itself with 
the application of deleterious substances (fungicides) to the host, 
in order that the germination and growth of the fungous spores 
may be prevented. This use of fungicides may take the form of 
disinfection of the seed or of propagative parts, the application of 
reagents to the soil in order to prevent the growth of the fungus 
in the vicinity of the host plant, or the application of fungicides to 
the aerial vegetative portions of the host, which is commonly acconl- 
plished by the operation of spraying. This latter operation has been 
practiced to a considerable extent for a long period of time, but the 
really substantial development of the work began with the discovery 
of Bordeaux mixture, to which reference has already been made. At 
the present time a great variety of spraying mixtures are employed, 
a large number of which contain copper compounds, or copper 
combined with lime, subsequently discussed in detail. There are, 
however, a great many directions in which the development of de- 
sirable fungicides may yet go forward. At the present time the 
use of lime-sulfur washes and sprays is rapidly taking an impor- 
tant place. It is particularly in connection with control measures, 
or facts concerning the life history of the organism suggesting such 
measures, therefore, that the study of fungous diseases of plants 
makes for itself a place among practical sciences. The amount of 
injury annually suffered by the various crops, due to fungous dis- 
eases, may be more or less definitely ascertained, and this repre- 
sents the possibilities to which control work may be pushed. On 
the other hand, the relation of the crop in unsprayed regions to that 
in regions where spraying is used may permit one more or less 
roughly to determine the actual saving through the present imper- 
fect and rather haphazard practice of control measures. Estimates 



8 FUNGOUS DISEASES OF PLANTS 

which have been placed upon the damage caused by prevalent 
l)lant diseases during a single season amount frequently to a very 
considerable per cent of the total value of the crops. In the United 
States alone the destruction wrought by fungous diseases is some- 
times not far from half a billion dollars. 

The diseases of plants induced by other biological, physical, 
chemical, or mechanical agencies are not included. The lack of 
plant nutrients, or the presence of particular nutrients in quanti- 
ties sufficient to cause injury, the phenomena commonly termed 
sunscalds, wind effects, abrasions due to contact, etc. are all dis- 
turbances which demand attention, but they may have no def- 
inite relation to epidemic fungous diseases, and would therefore 
be fundamentally considered only in a general treatise on plant 
pathology. On the other hand, it is felt that in connection with 
any account of the fungous diseases of plants it is desirable to 
place within easy reach of the student certain related information. 
In isolated chapters, therefore, there is presented a brief review 
of culture methods, histological technique, and such facts of physi- 
ological significance as seem requisite. 

Culture methods are here concerned with the essential steps in 
preparing important nutrient media and means for the isolation 
and study of fungi in artificial cultures. Such cultures are important 
in morphological and physiological study, and they afford in the 
majority of cases the only proper source of spores or mycelium for 
inoculation purposes. 

Histological technique is requisite not merely to insure a proper 
morphological study of a fungus and its distribution in the host, 
but also in order to make possible a more comprehensive analysis 
of the tissue modifications in the host. 

A discussion of special biological or physiological relations has 
been limited to a few topics. The germination of spores is from 
the outset one of the investigational or routine duties of the pathol- 
ogist ; the relations of the fungi to chief environmental factors 
cannot be disregarded; artificial infection is required in determining 
the causal organism ; and the principles of disease control are con- 
cerned with the immediate application of pathological study to 
economic purposes. 



PART I 

CULTURE METHODS AND TECHNIQUE 



CHAPTER I 

ISOLATION AND PURE-CULTURE METHODS 

LOEFFLER, Fr. Voilesungeii iiber die geschichtliche Entwickelung der Lehre 
von den Bakterien 1 : 252 pp. 3 pis. 37 figs. 1887. Leipzig. 

Smith, Erw. F. Bacteria in Relation to Plant Diseases. Carnegie Inst, of 
Washington, Publication 27 (Vol. I): 285 pp. 31 ph. i^jfigs. 1905. 

(Text-Books and Manuals of Bacteriology.) Nearly all texts on general bac- 
teriology devote considerable space to methods of culture work. 




Fig. I. View in Lakoratory equipped for Plant Physiology and 
Pathology. (Photograph by O. Butler) 

The student who is interested in the fungous diseases of plants 
will find it desirable at the outset to acquire a knowledge of pure- 
culture methods. The investigator in plant pathology can only pro- 
ceed confidently in his work when he has had practical training in 

9 



lO CULTURE METHODS AND TECHNIQUE 

the cultivation of fungi in the laboratory. This work has become 
increasingly more important in recent years. Laboratory culture 
methods were not generally applied to a study of the filamentous 
fungi until some years after bacteriology had been revolutionized 
by a series of important discoveries in this line of technique. It is 
at once evident that the bacteria could never be studied advanta- 
geously except through the establishment of pure-culture methods, 
whereas the larger fungi were to the early systematists and mor- 
phologists, organisms to be studied after the method applied to the 
higher plants and animals. Prior to the new era in bacteriology 
special methods were employed, it is true, in the germination of 
fungous spores, and some notable experiments in artificial infec- 
tion had been made. Nevertheless, after the introduction of pure- 
culture methods in general bacteriological work had become well 
established, plant pathologists were not slow to appropriate and, 
in certain directions, to develop a technique which promised and 
which has served to throw open the whole field of phytopathology 
to research of a high order. 

I. THE DEVELOPMENT AND APPLICATION OF CULTURE 

METHODS 

Note. The following are some papers of interest in connection with the 
early development of culture methods. 

Klebs, E. Beitrage zur Kenntni^s der Microcceen. Arch. f. Exp. Path. u. 

Pharmakol 1 : 31-64. 1873. 
COHN, F. Untersuch. iiber Bacterien. Beitrage zur Biol, der Pflanzen 2 : 240- 

276. 1876. 
Lister, Jos. On the Lactic Fermentation and Its Bearings on Pathology. 
Trans. Path. Soc. London 29 : 425-467. 
(Dilution methods for obtaining pure cultures, see p. 445.) 
KoCH, RoBT. Zur UnterSuchung von pathogenen Organismen. Mittheil a.d. 
Kais. Gesundheitsamte (Berlin) 1 : 1-48. p/s. 1-14. 1881. 
(Poured plate and streak method first described.) 
Petri, R. J. Eine Kleine Modification des Kochschen Plattenverfahrens. 
Centrbl. f. Bakt. 1 : 279-280. 1887. 
(Description of the now common Petri dish.) 

Rapid development in isolation technique. The most fruitful 
principles involved in bacteriological culture methods were the 
outcome of work throughout not much more than a dozen years, 
practically between 1873 and 1885. On the other hand, the bio- 
logical facts encouraging and inspiring investigation in this field 



ISOLATION AND PURE-CULTURE METHODS ii 

had long been accumulating. More than a century prior to the 
dates mentioned, Bonnet and Spallanzani showed some apprecia- 
tion of the principles of sterilization and they were more or less 
successful in attempting tcr demonstrate that when the organisms 
in any given nutrient medium are killed, an entrance of germs 
from without is necessary in order that growth may subsequently 
occur. Nevertheless, belief in the infelicitous idea of spontaneous 
generation gained strength, and was not finally abandoned by some 
prominent scientific men until after the great conquests made by 
Pasteur and others in the fields of fermentation and disease. An 
important era was marked by Cohn's demonstration that the spores 
of many bacteria are particularly resistant to heat, and that it is 
only after passing into the vegetative condition that boiling may 
effectually kill such organisms. This led promptly to the adoption 
of a discontinuous method of sterilization, and thus it became a 
matter of easy manipulation to grow organisms in media rendered 
absolutely sterile. 

It was in 1873 that Klebs described a "fractional" method of 
isolating bacteria, and Lister five years later developed a " dilu- 
tion" method. Viewed in the light of to-day these methods were 
burdensome, yet they were not impossible in the hands of careful 
workers. The methods adopted were necessarily extremely crude 
in comparison with those employed to-day. The dilution process 
was the surest practical method of isolating yeasts and bacteria. 
This method consisted essentially in diluting to such extent, in the 
beaker or other vessel of sterile water, a drop of any fluid con- 
taining the organism so that a drop of the diluted material would 
contain, perhaps, not more than a single cell or organism. This 
dilution was, of course, based upon a tedious count made under the 
microscope. If, then, drops of this water in which the organisms 
or cells were suspended should be transferred one to eagh of sev- 
eral tubes containing any desired medium, a separation might be 
effected. Drops of the liquid containing the organisms might also 
be spread on the surface of a sterile slice of potato, and, with growth, 
separate colonies might appear. This was practically the status of 
methods which had been developed for the isolation of microscopic 
organisms, up to about 1881, which date marks the beginning of a 
very distinct advance. 



12 CULTURE METHODS AND TECHNIQUE 

Isolation by means of solid media. Credit for the sudden perfec- 
tion of isolation methods is due to Robert Koch. He had watched 
to good advantage the difficulties in the way of securing isolated 
colonies of bacteria on potatoes, or by the older methods, and in 
search of a more desirable medium, he began experiments in a 
wholly new field. The outcome of his researches was the substi- 
tution for potatoes of a substance which would have both liquid and 
solid properties. This substance he found first in gelatin and later 
in agar agar. Either of these could be employed in his simple and 
efficient poured-plate isolation method. The results of those studies 
have given us a powerful equipment for the study of the fungi as 
well as the bacteria. The substitution of Petri dishes for plates, 
and many refinements in the way of sterilization apparatus followed 
promptly. 

Mycological advances. Meanwhile valuable contributions had 
been made by De Bary, Brefeld, and others, serving to stimulate 
research along purely mycological lines. The employment of syn- 
thesized media, improvements in the general methods of making 
nutrient media, and the use of diverse plant products have brought 
into the work, on the one hand, the development of definite stand- 
ards, and, on the other, the possibility of cultivating forms once 
prevailingly thought to be specialized parasites. The recent devel- 
opment and application of culture methods from the phytopatho- 
logical standpoint has been such as greatly to stimulate renewed 
interest in systematic mycology, and the physiological aspect of the 
work has been notably advanced. In fact, the physiological studies 
of the past ten years have been to a very commendable degree 
studies in the physiology of the fungi. The simplicity of form, the 
great variety in species and in habitats, the readiness of growth in 
pure culture, and the rapid response to stimuli all unite to make 
these plants favorable material for investigation and demonstration. 

H. CLEANINC; (;lassware 

Even for ordinary purposes in culture work glassware should be 
thoroughly cleaned. Any reagents which will conveniently accom- 
l^lish the purpose may be used, but the general methods followed 
in bacteriological laboratories are to be advised. Special methods 
will be necessary in certain cases and here one's knowledge of 



ISOLATION AND PURE-CULTURE METHODS 13 

chemistry must direct. Ordinarily it is not enough to depend upon 
hot water and soap in cleaning glass vessels. Petri dishes, test 
tubes, etc., may be boiled for a short time prior to cleaning, and if 
grease is present, a small quantity of potash lye (about 30 grams 
per liter) may be added. If the glassware is immersed in water, a 
porcelain-lined vessel should be used, and the latter may be placed 
over the flame or in the steam sterilizer. Commercial hydrochloric 
acid is convenient in many cases for general use. A chromic acid 




Fig. 2. Some Chief Types of Glassware required in Student Culture 
Work. (Photograph by Geo. M. Reed) 

cleaning mixture has also become quite generally adopted and gives 
excellent results. This mixture may be made sufficiently strong for 
ordinaiy purposes by dissolving 100 grams of potassium dichromate 
in 1000 cc. of hot water, then when the salt is all dissolved and 
the liquid cool, pour into it about 500 cc. of strong sulfuric acid, 
stirring constantly. This liquid should be stored in large-mouthed, 
glass-stoppered bottles, and used with care. It may be used repeat- 
edly. When employed, it may act for from ten minutes to twenty- 
four hours, and it may be followed by water, or soap and water, 
etc. This mixture is not convenient to handle but is very effective. 
Test tubes. Ordinarily these should be cleaned with hot water, 
soap and a test tube brush ; and this cleaning may be preceded or 



14 CULTURE METHODS AND TECHNIQUE 

followed by the potash solution or the cleaning mixture, as occasion 
may demand. In either case the tubes are thoroughly rinsed ulti- 
mately with distilled water, the outside of each wiped dry, and 
they are then placed upon a test tube rack. In order that they may 
dry rapidly and without blemish, they may be rinsed with 95 per 
cent alcohol. A considerable quantity of alcohol may be used in 
the first tube, the top of which when shaken is closed with the 
finger. The same alcohol may thus be used for twenty or more 
tubes successively. Tubes containing agar, or old cultures, are more 
easily cleaned after being boiled for some time in the steam steril- 
izer or in the autoclave. 

Petri dishes. These are generally cleaned with hot water and 
soap. They should be thoroughly rinsed in clean, hot water and 
wiped while yet hot. It is seldom necessary to leave cultures, or 
the agar employed in cultures, in these dishes until the medium 
becomes hard and dry. If so, it may be essential to soak or steam 
the dishes a long time before cleaning. 

Flasks. It is difficult to get at the interior of flasks with any 
type of brush, whereas reagents are readily employed in cleaning 
such apparatus. The chromic acid mixture should then be employed, 
and afterwards the flasks are rinsed and treated with alcohol as for 
test tubes. If the flasks are desired for immediate use, after the 
alcohol treatment, they should be rinsed with a small quantity of 
ether, and may then be rapidly dried with a blast or foot bellows, 
if one is convenient. 

Slides and cover glasses. When new, or when stained, these 
may be effectively cleaned by the chromic acid mixture, in which 
they should remain from twelve to twenty-four hours. They are 
next rinsed, and the slides wiped directly, while the covers should 
be wiped with cheese cloth or linen after a transfer to alcohol. 
When the slides are soiled with paraffin, wax, vaseline, or other 
oily material, boiling in the potash solution or in carbonate of soda 
will be necessary. The same treatment should be used for tubes 
sealed with paraffin. Balsam preparations are cleaned by soaking 
for some time in 75-90 per cent alcohol, and then by rinsing in 
waste xylol, benzine, or other such solvent of the balsam. 

Special methods. For studies in nutrition, germination experi- 
ments with special stimuli, and other very careful physiological 



ISOLATION AND PURE-CULTURE METHODS 15 

work, it is necessary to have glassware which is not only clean with 
relation to extraneous substances, but which is as far as possible 
free from the soluble substances which may be contained in the 
glass itself. In the first place, it is well to have vessels of Jena or 
of the best Bohemian glass. Such glassware may be first cleaned 
by the ordinary process. This is followed by boiling in the potash 
or other alkaline solution. The vessels are then rinsed and boiled 
in weak hydrochloric acid, and rinsed again. Finally, they are filled 
with distilled water and steamed for a number of hours. 

In this connection it may be said that cover glasses which have 
been perfectly cleaned and dried will give more trouble in the 
preparation of hanging drop cultures than those less perfectly 
washed. On the former there is a tendency for the drop to spread 
or to shift its position at the slightest movement. Loss of stability 
in the drop should, however, be sacrificed to absolute cleanliness 
if one is doing quantitative work. The drop will have even a 
greater tendency to spread if the cover glasses are flamed imme- 
diately before being used. To avoid this latter difficulty, if wiped 
with a clean sterilized linen cloth and placed in a sterile Petri dish 
just as they are taken from the alcohol, there will be practically no 
danger of contamination. 

Cover glasses which are to be used in making preparations of 
bacteria should be absolutely clean, and the method above mentioned, 
namely, boiling in an alkali, in acid, and in distilled water is requi- 
site. They should be air-dried from strong alcohol. Thus prepared, 
the covers will permit the operator to spread uniformly over the 
surface a drop containing bacteria. 

in. THE PRINCIPLES AND METHODS OF STERILIZATION 

Vessels and media. Sterilization, as the term is generally em- 
ployed, is merely the process of killing all of the organisms or 
spores which may be present in a medium or vessel or upon a 
given object. In culture work sterilization, therefore, is more par- 
ticularly employed when a substance or vessel is to be used for 
the culture of a particular organism, or to preserve nutrient media 
from decomposition. The common and most "effective method of 
sterilization is by means of heat. Some important uses of chem- 
ical agents in sterilizing are not here considered. Steam heat or 



1 6 CULTURE METHODS AND TECHNIQUE 

dry heat may be used, depending upon the nature of the medium 
or object to be sterihzed. Liquids or any soHds wliich may melt, 
evaporate, or dry out in a dry atmosphere require moist or steam 
heat ; while all heat-resistant diy apparatus and glassware, and well- 
dried solids, such as sand, glass wool, etc., usually require dry heat. 
Sterilization at lOO° C. When steam heat is used, sterilization 
is often given at the boiling point of water. Sterilization may thus 



1 


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Fig. 3. On the Right, Arnold Steam Sterilizer; on the Left, Lauten- 

SCHLAGER HoT AlR STERILIZER; BOTH UNDER HOOD 

be effected in an ordinary boiler, or over a water bath. Steam 
sterilizers of various patterns are now made, which accomplish this 
work most effectively, and they should be in use in all laboratories. 
The two general types of sterilizers in common use are those 
which bear the name of Koch and Arnold. The latter are simpler 
in design and less expensive. Fig. 3 shows a good form of this 
sterilizer. From the diagram, Fig. 4, it will be seen that the water 



ISOLATION AND PURf:-CULTURE METHODS 



17 




Fig. 4. AuNOLi) Steam Sterilizer, 
Square Tyi'e, showing Construc- 

TKJN 



in the chambered bottom is rapidly brought to the boihng point, 
and then the gradual entrance through the holes of water from the 
reservoir will supply the boiler for several hours, if it is necessary 
to employ it so long. 

The Koch sterilizer is now less used. Aside from being a well- 
made piece of apparatus, it has only the advantage that the regulation 
of the water supply is automatic. 
It is expensive and is only espe- 
cially desirable in case of steriliza- 
tion or digestion for many hours. 

Countless experiments have 
shown that while the vegetative 
cells of most bacteria are usually 
killed by a single sterilization of 
from fifteen minutes to one hour 
at 100° C, yet the spores of many 
forms are not killed by one ex- 
posure at this temperature. As a 
matter of fact, an exposure for 
a few minutes at 100° C. in the steam sterilizer is usually suffi- 
cient to kill the growing parts of most fungi. It is not, however, 
such delicate parts which are to be reckoned with in the sterilization 
of nutrient media, but rather the resistant spores of fungi and bac- 
teria, and thick-walled mycelial parts. Forms which are strongly 
heat-resistant may often be encountered in the preparation of such 
media as potatoes and manure decoction. 

To Cohn is due the notable discovery of heat-resistance in the 
spores of bacteria, and logically following this Tyndall demonstrated 
the necessity of discontinuous or successive sterilization, after in- 
tervals sufficiently long to permit such organisms, or parts of organ- 
isms, as have remained as spores to germinate, and therefore to be 
more readily killed at the next heating. In general, it is necessary 
to sterilize on three successive days. As is well known, when one 
is careful in making the medium a single sterilization of half an 
hour is usually sufficient for tubes of agar, if tlie apparatus has 
not become infested with particularly resistant spores. In no case, 
however, should one depend upon a single sterilization unless the 
material is to be kept several days previous to inoculation. Stock 



1 8 CULTURE METHODS AND TECHNIQUE 

quantities of media should be sterilized three times. Between the 
periods of sterilization media should be placed at a temperature 
favorable for most bacterial development, and not in a cold place, 
this being in order that any spores might pass into the vegetative 




Fig. sa. Autoclave, Erect Type, Clamped Top, heated by Gas 
(Photograph by Geo. M. Reed) 

State within twenty-four hours, and thus be killed at the next 
sterilization. 

A suggestion which has been made by Theobald Smith is of 
interest in connection with the sterilization of media which may con- 
tain anaerobic bacteria. If such media are sterilized in thin layers, 
oxygen may have comparatively free access to any submerged 



ISOLATION AND PURE-CULTURE METHODS 



19 



spores, and consequently they may not germinate between the 
successive sterihzations. On the other hand, if the medium is 
deep in the vessel, and the exposed surface of the medium small, 
much less oxygen gains access, and the spores of anaerobic forms 
pass more readily into the vegetative condition and are killed by 
the successive sterilizations. 

Sterilization under pressure. A great time-saving convenience 
in sterilization is to be found in the use of the autoclave, or steam 





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.- . mi\ 


m/\ 


r 


-^^E"^^ 


'_/l 


fl 


WM '%i^W ■ P 


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Fig. 5^. Autoclave, Horizontai, Type, connected with Steam Pipes 
(All steam apparatus under a hood) 

pressure sterilizer, two types of which are shown in Fig. 5, a and d. 
The autoclave is not only more effective than the ordinary steam 
sterilizer, but by using it the delay of discontinuous sterilization is 
avoided.. In this apparatus the steam is confined, up to any pres- 
sure desired, instead of being allowed to escape, as in the ordinary 
steam sterilizer. A good steam pressure gauge on the autoclave 
is requisite, and a thermometer is not only desirable, but also an 
additional safeguard. The temperature ordinarily employed is 115° 
to 125° C, or about 10 to 20 lbs. pressure. A single incubation 



20 CULTURE METHODS AND TECHNIQUE 

of from fifteen to twenty minutes at this temperature will usually 
sterilize any medium. The period of incubation must of course be 
measured from the time the desired temperature is attained, and it 
may require from ten to fifteen minutes, even with a strong burner 
system, in order to reach this temperature. An autoclave contain- 
ing an ordinary amount of culture vessels should, if provided with 
a double ring of burners, and jacket, develop a pressure of 1 5 lbs. 
in about ten minutes. 

Temperatures higher than 115° may transform, possibly through 
acidity, many sugar-containing and other organic media, and con- 
sequently greatly reducing their value for the growth of many 
organisms. Gelatin and milk are injured, if acid, by autoclave tem- 
peratures. With more readily decomposable substances sometimes 
necessarily employed in phytopathological work, it may be possible 
to effect sterilization at temperatures below the boiling point, at 
from 80° to 90° C, say, sterilization being made on about six suc- 
cessive days. The blood serum incubator may also be employed. 

Not only does the autoclave facilitate sterilization, but it is eco- 
nomical in the preparation of media to such an extent that it should 
be in general use. The expense of such a piece of apparatus is the 
one factor operating against its general adoption, yet a good instru- 
ment handled carefully should last a number of years. 

The autoclave may be heated by burners, or it may be connected 
with a steam supply pipe, if a supply of steam under sufficient 
pressure may be constantly at hand. Autoclaves are usually pre- 
pared for gas burners. In using this instrument care should be 
taken to arrange mechanical reminders if there is danger of its 
being neglected even for half an hour. It might be suggested that 
an alarm clock as such is useful, or that a clock arrangement for 
shutting off the gas at the desired time is in use in some labora- 
tories. With the gas-heated autoclaves, particularly, certain precau- 
tions are necessary. Before each sterilization it must be noted that 
sufficient water is present, usually up to the crate or false bottom ; 
and it is well to employ distilled water. The lid and other fittings 
should be kept free of dirt and dust, so that all fastenings may be 
tight and secure. If the burner capacity is not too great, the gauge 
screw may with little practice be set at the temperature desired, the 
steam vent left open, and the apparatus lighted. A few minutes after 



ISOLATION AND PURE-CULTURE METHODS 2 1 

steam begins to escape vigorously, or practically as soon as the 
thermometer registers ioo° C, the vent is closed. It is not advis- 
able to leave the autoclave without observation during sterilization, 
since there are many chances for mishaps ; nevertheless, if the 
safety valve is set for a given pressure, steam will, of course, be 
blown off at about the temperature desired. This blowing off of 
steam is a good signal for cutting off a part of the gas supply, as 
the rapid escape of steam not only results in exhaustion of the small 
reservoir, but often dislocates the cotton plugs. When the time 
for sterilization has elapsed, the gas is turned off ; but the steam 
vent should be only gradually opened as the pressure falls to o° C, 
else the medium may boil over and the plugs will be blown out of 
the vessels. If steam is used instead of a gas burner, a complicated 
set of stop-cocks will be required, or will at least be advantageous, 
to regulate the inlet and exit of the steam. 

Hot ah- sterilization. Implements, glassware, cotton, sand, and 
other vessels or materials used in culture work, which may not be' 
sterilized by steam or by the burner flame direct, are sterilized in 
a hot air sterilizer. It is true that the delicate mycelium and spores 
of many fungi are often injured or killed by drying alone ; yet, on 
the other hand, the spores and mycelium of many fungi are ex- 
tremely resistant to desiccation and to a high degree of dry heat. 
By long practice it has been ascertained that it is not safe to attempt 
to sterilize vessels in a dry oven at less than 1 50° C. for one hour, 
or at a slightly lower temperature with protracted sterilization. Test 
tubes or flasks plugged with cotton, or Petri dishes wrapped with 
paper, cannot well be exposed to a much higher temperature. 
Glassware may safely be exposed to a temperature of 170° C, or 
higher. The best form of hot air sterilizer is the Lautenschlager, 
Fig. 3, yet a simple and inexpensive oven will suffice. 

Sterilization of soiL In all inoculation work where there is 
danger of contamination from the soil, and particularly in the study 
of root and stem diseases, experiments with damping-off fungi, and 
the like, it is necessary to use sterile soil and sterile pots. The 
pots may be prepared with soil as for the growing of any plants, 
well watered, and then sterilized a few at a time in any steam ster- 
ilizer or autoclave. In the former they should be sterilized at least 
two or three hours after the temperature has reached 100° C, and 



2 2 CULTURE METHODS AND TECHNIQUE 

this should be repeated if possible the next day. This method is 
available when there is only a small number of pots to be handled. 
When, however, the work must be conducted on a larger scale 
an effective apparatus is the Britton soil sterilizer. Britton has 
described ^ a steam sterilizer for soils which he has devised for use 
in the station greenhouses. This apparatus is simple and seems to 
be wholly practicable. It is described as follows : 

It consists of a square box made of heavy galvanized sheet-iron connected 
with the steam-heating system in the potting room of the forcing-house (or 
elsewhere convenient). This box is cubical in form, each of its three dimen- 
sions being thirty inches ; six inches of the top is in the shape of a removable 
cover. Steam enters through a hole in the center of one side, to which side is 
soldered a coupling. A three-fourths inch pipe, fitted with a valve, connects 
the apparatus with the steam-heating system. A few strips of wood placed 
under the box raise it a half inch from the cement floor to prevent rusting. 
Inside the metal box are similar strips upon which the trays rest. Two small 
holes in the bottom allow the condensed water to escape. 

The soil is placed in the trays which are made of wooden frames having 
bottoms of galvanized wire netting. The frames are made of strips of wood 
three and one-half inches wide and seven-eighths of an inch thick ; after fasten- 
ing the netting, a half-inch strip is nailed on to hold the netting firmly and to 
cover its jagged edges. The dimensions of the trays in inches are 27 x 13 x 4 
over all, and inside are 251x11^x3^ inches. 

The wire netting has six meshes to the inch. Soil is spread loosely and 
evenly in the trays to the depth of about three inches and the trays packed 
inside the metal box in cob-house fashion. . . . 

There is a space of one and one-half inches all around the trays inside the 
box, and a space of an inch between the two trays. The half-inch strips on the 
bottom edges of the trays allow the steam to enter above and below the coil 
in each of the trays. As the steam comes in contact with the soil, both above 
and below it, much less time is required to heat it than when in a solid mass. 
The sterilizer contains fourteen trays, which, when filled to the depth of three 
inches, hold 6.9 cubic feet of soil. . . . Steam entering through a three-fourths 
inch pipe at a pressure of five pounds per square inch, heats the soil to the 
boiling point of water in about fifty minutes — a great deal depending, of 
course, on the density of the soil, as a loose soil heats through much more 
rapidly than if packed closely. The box is not steam tight, but nearly so for a 
low pressure ; considerable expense would be necessary to make it perfectly 
steam tight and at the same time permit of convenience in opening the box. 

Soil was kept in the apparatus one hour for the purpose of killing the nem- 
atodes. This also doubtless destroyed many fungous germs, but where absolute 

1 Britton W. E. A Steam Sterilizer for Soils. Conn. (New Haven) Agl. Exp. 
Sta. Report (1897): 310-312. 



ISOLATION AND PURR-CULTURE METHODS 23 

sterility from bacteria and fungi is desired it would be necessary to steam the 
soil for a much longer time. The steamed soil is also almost wholly free from 
live seeds of weeds while the untreated soil was considerably infested with vari- 
ous common weeds. 

A Sterilizer may be arranged more or less after this pattern, but 
with particular reference to the conditions at hand, A sterilizer of 
this type may also be used for pots and saucers already filled with 
soil. A better pressure of steam may be secured, of course, if the 
sterilizer is directly connected with the boiler. For summer work, 
moreover, it is not desirable to have the sterilizer connected with 
the general heating system. 

Soil sterilized by dry heat requires a very high temperature, and 
is unquestionably somewhat injured in the process. On the other 
hand, it must be remembered that soil which has been steam-ster- 
ilized encourages upon reinfection the growth of such saprophytic 
organisms as Mucor and Penicillium, and possibly such hemisapro- 
phytes as Rhizoctonia and other fungi causing root diseases. Care 
must be taken, therefore, not to permit these organisms to get a 
start in the soil before normal bacterial action has begun. 

IV. PREPARATION OF CULTURE MEDIA 
Liquid Media 

Except in investigations where a medium of known composition 
is required, or in drop cultures and the like, liquid media are less 
used for cultural purposes with the fungi than with the bacteria. 
In many physiological studies, however, such media are desirable 
or indispensable, and as a rule these liquid media form the nutrient 
bases for the making of most of the gelatinous solid media employed 
in mycological work. 

Plant decoctions are undoubtedly of the first value for work 
with the fungi, and with these organisms they may entirely replace 
bouillon, considered so essential in the culture of bacteria. Some 
of the most nutritious and convenient plant decoctions may be made 
from the sugar beet, white potato, carrot, pods and stems of bean, 
or vetch, prunes, apples, celery, and various other plants or plant 
products. In order to secure more or less uniformity in the com- 
position of these decoctions, for every 1000 cc. of water used it 



24 CULTURE METHODS AND TECHNIQUE 

has been my practice to require 50 grams dry weight of the plant 
product. Accordingly, from a mean of several analyses brought 
together, it would require about 490 grams of beet root, 400 grams 
of bean stems or of string beans, 1 20 grams of dried prunes, and 
about 390 grams of the fresh potato. 

The plant product is washed, and, if desirable, pared, cut up 
finely, or thinly sliced, and then the necessary water is added. It 
is next boiled in the steam sterilizer for about two hours, or in the 
autoclave at 1 1 5° C. for twenty minutes. If necessary to boil over a 
steam bath, a flask plugged loosely with cotton, or a small-mouthed 
agate pitcher covered with flannel, should contain the material, so 
that a minimum of evaporation will occur. The clear liquid is filtered 
off through several thicknesses of filter paper into a sterile flask, 
when it may be immediately used in making solid media, or ster- 
ilized as usual for preservation. Where it is particularly desired 
to obtain the clearest decoction possible, the liquid may be cooled 
to about 60° C. under the tap, or by pouring from one vessel to 
another, and then the white of an egg may be added. The decoc- 
tion is again boiled for an hour in the sterilizer, or about fifteen 
minutes in the autoclave ; and the clear liquid finally filtered away 
from the coagulated albumen and sediment. 

It will often be necessary, or well, to make decoctions of various 
other plants, particularly of fleshy fungi, of the host plants upon 
which certain fungi grow, etc. Such decoctions may be particularly 
desirable in physiological work. 

Manure decoctions of any kind are particularly serviceable in the 
study of many saprophytic organisms, but in pathological work 
these liquids are no more valuable than any of the plant decoctions. 
Special emphasis might be laid upon prune juice, or prune decoc- 
tion, es]3ecially when the fungus is one w^hich may inhabit saccha- 
rine fruits, berries, etc. 

It will be readily suggested to the student that plant products 
of various kinds may be roughly grouped into such as are rich in 
albumens, starches, sugars, etc., and these products will be selected 
and employed in accordance with such indications with respect to 
the needs of the fungxis as are available. 

Bouillon, the chief fluid medium used for the bacteria, is an 
extract of beef, practically a beef tea, to which peptone is added. 



ISOLATION AND PURE-CULTURE METHODS 25 

It is usually made directly from lean beef, and is an infusion of 
the beef in twice its weight of water. To prepare it, 500 grams of 
lean meat, as free as possible from fat, are chopped or ground 
finely, and to this is added 1000 cc. of distilled water. It is then 
placed in a cool place for twelve to fifteen hours, and occasionally 
stirred, if possible ; or it may be placed in a water bath at 65° C. 
and frequently stirred for a period of about one hour. By the latter 
method the bouillon is said to contain some less desirable substances, 
but it will often be found the more desirable process for students 
who cannot be at the laboratory regularly. All of the juice possible 
should be squeezed out of the meat, and a hand press is frequently 
used by bacteriologists to accomplish this more effectively. The 
red liquor filtered off through cheese cloth is made up to one liter 
with water, and then to it is added 10 grams of peptone and 5 grams 
of sodium chloride. It is then heated in the steam sterilizer for 
one hour, or in the autoclave fifteen minutes, when a clear liquid 
with a well-differentiated coagulum is to be seen. This is filtered' 
readily through filter paper. The bouillon will now be slightly acid 
and should be neutralized or given the desired reaction with sodium 
hydrate (see page 33). For ordinary purposes with fungi it may 
be enough to use the litmus paper test, but special methods of 
neutralization are essential in the most careful work either with 
fungi or bacteria. These must be adhered to for accurate physio- 
logical work, or for furnishing descriptions of the fungus on specified 
media. If the bouillon is not perfectly clear, an egg also may be 
used as with the plant decoctions, to effect clarification. The medium 
is next sterilized and preserved. Prepared meat extracts are used 
by some in making bouillon. 

Milk and litmus milk are only important with the bacteria. 
P^resh milk alone should be employed, and from this the cream 
should be removed either by the centrifuge or by standing. Litmus 
milk is made by the addition of 2 cc, of a saturated solution of blue 
litmus to each 100 cc. of milk. This is extremely sensitive to the 
development of alkalis or acids during the growth of organisms. 

Synthetic liquid media, as they are termed, that is, media pre- 
pared by the use of salts, carbohydrates and other substances of 
known composition are more extensively used in physiological work. 
There the specific purpose of the experiment should be depended 



26 CULTURE METHODS AND TECHNIQUE 

upon to determine the composition. These media are, however, 
important in all culture work. The following solution has been in 
such common use as to be generally designated a standard nutrient 
solution : 

Ammonium nitrate i.o gram 

Dihydrogen potassium phosphate 5 gram 

Magnesium sulfate 25 gram 

Iron chloride trace 

Cane sugar 5-° grams 

Water 100 cc. 

With some fungi the addition of a small quantity of sodium chloride 
is advantageous. 

Among the many other culture fluids which have been used, 
one of the most important available alike for fungi and bacteria, 
although not ideally constituted, is Uschinsky's solution, made of : 

Ammonium lactate 6-7 grams 

Sodium asparaginate 3-4 grams 

Potassium hydrogen phosphate 2-2.5 grams 

Magnesium sulfate 0.3-0.4 grams 

Sodium chloride 5-7 grams 

Calcium chloride o. i gram 

Glycerin 30-4° grams 

Distilled water 1000 cc. 

Experience in culture work will promptly demonstrate that the 
concentrations of the above solutions are to be regarded as impor- 
tant because they establish standards. In special cases, however, 
it may be desirable to increase considerably the amount of carbo- 
hydrate, and this, in turn, may render desirable further changes. 

Solid Media 

Nutrient agar agar. Agar, or agar agar, is a substance some- 
what of the nature of gelatin. It is, in fact, a kind of gelatin, or 
glutinous substance, made from ceitain seaweeds, especially species 
of Gclidmni (Fig. 6) or Gloiopcltis, which grow abundantly on the 
coasts of Japan and China. The commercial article is usually ob- 
tained in the form of shred-like strips, or as a powder. Agar has 
this advantage over gelatin, namely, that at a suitable strength it 
will remain solid up to a temperature of at least 45° C, and it 



ISOLATION AND PURE-CULTURE METHODS 



27 



very seldom becomes liquefied by the action of growing organisms. 
Nutrient agar agar consists of some nutrient "base," like sugar 
beet or prune decoction, bouillon, etc., to which is added, for pur- 
poses of solidification, 11 to i 5 grams of the commercial agar agar 
per liter. The nutrient base, whether plant decoction or bouillon, 
may be made as already indicated. There are then several methods 
of procedure for making the agar, (i) When an autoclave is at 
hand, 12 grams of the agar are merely cut up finely into a liter 
of the desired decoction and this is placed in the autoclave and 
Steamed at from 1 10° to 1 1 5° C. In thirtv minutes the agar will be 




Fig. 6. UhLiiuLM lOKXi CM Lam., Furnishing Agar Agar 
(After Erw. F. Smith) 

dissolved. It is then neutralized, or brought to the desired reaction ; 
and if not clear, the white of an %^g may be added, as' usual, when 
a second similar or shorter steaming is necessary. (2) This same 
method may be used with the steam sterilizer, except that it may 
require from one to two hours for the complete solution of the 
agar. Some grades of agar dissolve very slowly by this method, 
and it is often recommended in such a case to soak the agar pre- 
viously twelve to eighteen hours in water containing sodium chlo- 
ricje. (3) Many find it more convenient to put the agar into an 
agate iron cup, add about 200 cc. of distilled water and boil directly 
over a flame, stirring constantly, until the agar is thoroughly dis- 
solved. This is then added to the decoction to be used. This last 



28 CULTURE METHODS AND TECHNIQUE 

method requires more of the personal attention of the operator, but 
it insures successful solution of the agar. The medium may be 
then cleared in the usual manner. 

In making nutrient agar, a chief difficulty for the beginner has 
been with relation to filtration, which is necessary in order that a 
clear product may be obtained in which the development of micro- 
colonies may be carefully followed. If the agar is thoroughly dis- 
solved, it filters with comparative ease ; whereas, if partly dissolved, 
filtration is next to impossible. In any case a grooved or ridged 
filter, good filter paper wet with hot water immediately before using, 
and well-dissolved agar direct from the pan, steamer, or autoclave 
are the requirements. Nevertheless, in case of difficulty, the filter 
stand with funnel and flask may be placed in the sterilizer or auto- 
clave to be kept thoroughly hot during the process. Again, a side- 
neck filter flask may be used so that connection with a filter pump 
attached to the tap may be secured. In the latter case porcelain 
supports and cotton may be substituted for filter paper. 

After filtration the agar may be poured into flasks or test tubes 
(usually about 8 cc. per tube, when used for isolation cultures), 
subsequently sterilized and stored. 

A synthetic liquid medium may be used as a nutrient base with 
agar. The standard salt solution previously mentioned and many 
others are serviceable ; however, since agar is a medium the com- 
position of which is complex, it is often too " impure " as to known 
qualities for certain physiological studies. Long washing is of value, 
but this may not remove all materials furnishing food substances. 
A few drops of hydrochloric acid in the water will also materially 
improve the purity of the agar, but it may injure or entirely destroy 
the solidifying properties. In most instances it is best to substitute 
for the agar Winogradsky's silicate jelly, or resort to cultures on 
tightly folded bars of filter paper or some other pure substance. 
Glycerin agar is particularly serviceable in culturing slow-growing 
fungi. It is made by the addition of 5 per cent glycerin to the 
prepared medium. 

A stiff agar, made by using from twenty to thirty grams of agar 
for each liter of solution, is desirable when cultures are to be trans- 
ported. It is also valuable, employed in large flask cultures, in 
order to obtain the fruiting stages of many fungi. 




ISOLATION AND I'URE-CULTURE METHODS 29 

Nutrient gelatin is employed extensively in the cultivation of 
bacteria, but seldom with the fungi. It is made by adding 100 
grams of gelatin to each 1000 cc. of bouillon. In the preparation 
of this medium one must use as little heat as possible. It dissolves 
readily in hot bouillon, and 
filters much more quickly 
than agar. The congealing 
properties of gelatin are de- 
stroyed by a long exposure to 
a greater temperature than 
io6°C., so that if the autoclave 
is employed, then the gelatin 
should be cooled promptly. 
When sterilized, the periods 
of steaming should not exceed Fig. 7. Double-Walled Metal Box for 
ten or fifteen minutes. Gela- Storage of Gelatin Cultures; con- 

nected with Water Supply. (After Novy) , 
tin melts at a temperature 

above 35° C. and often lower, so that it must be stored in a cool 
place ; and the cold water box of Novy (Fig. 7) may be used to afford 
such a low temperature when the refrigerator is unsatisfactory. 

Starch jelly should become an important nutrient medium. It 
can be obtained fairly pure, and in connection with synthetic salt 
solutions it is valuable for slanting tubes. Commercial starches 
generally contain resistant spore-forming organisms, and it is desir- 
able to shake up the starch in a flask with 95 per cent alcohol for 
one hour and dry rapidly on filter paper before using. A 10 per 
cent mixture in the salt solution selected should be made. Rub this 
up well before heating, and sterilize, if possible at from 90° to 93° 
C. on successive days. 

Vegetable products. Cylinders or slices of vegetables, such as 
the sugar beet or potato, or even young stems or pods of bean, 
prunes, squash, corn meal, etc., prove excellent media of different 
types, most suitable for work with the fungi. The sugar beet is an 
excellent general medium, rich in cane sugar. It is quite generally 
obtainable during the autumn, and laboratories may then be pro- 
vided with a supply which will keep in a cellar over winter. The 
potato is always available and offers an excellent starchy medium. 
The stems or young pods of bean are rich in nitrogenous material, 



30 CULTURE METHODS AND TECHNIQUE 

but in the preparation of these more care is necessary for the pre- 
vention of bacterial contamination. This is one of the most nutri- 
tious culture media known for fungi in general. String beans may 
be obtained on the market at almost any season. Celery leaf stalks 
are a medium rich in nitrates and desirable for some organisms. 
All of these highly nutritious media are excellent for securing the 
vegetative growth of an organism, but it is very often the case 
that with such media fruiting stages are not obtainable. I have 
almost invariably obtained better fruiting stages by using ordinary 
corn meal, or maize meal. This can be prepared to advantage in 
small flasks. The flask is filled with meal to a depth of about two 
thirds of an inch. This is then wet with water, hot water being 
preferable, as cold water does not wet it so readily ; and enough 
water is added to make the meal quite soft, since considerable water 
will be absorbed during sterilization. Cylinders or plugs of various 
root crops, or stems of plants, dead wood, and various other products, 
may serve special purposes. 

In preparing the cylinders of root crops, the roots should be 
thoroughly washed and pared, and then cut into pieces of desired 
size. If used in a test tube, a scoop which cuts out a cylindrical 
piece will be found convenient. These cylindrical plugs, say three 
inches long, are then cut diagonally. Ordinarily a piece is placed in 
a test tube of 1 2 — 1 5 x 1 50 — 1 80 mm., and then ^ to i inch of 
water is added. More desirable for many purposes, and particularly 
for transportation, is to put in each tube half an inch or so of satu- 
rated absorbent cotton, and within this rests the end of the nutrient 
substance, which is thus firmly held in place. The latter method 
avoids all fluids in the cultures, and the tubes may be inclined or 
placed upright afterwards, as convenient. In somewhat the same 
way wads of absorbent cotton or of filter paper may be placed in 
the tubes, and these wads then moistened or wet with any nutrient 
solutions desired, and subsequently sterilized. Closely folded pieces 
of filter paper may be used in this way with solutions of known com- 
position for very accurate work in nutrition ; and in such cases a 
supply of the liquid may also be placed in the tube so that the 
culture may not dry out for a considerable period. 

It is often desirable, and indispensable for the best growth, to 
use in connection with a culture liquid of known composition some 



ISOLATION AND PURE-CULTURE METHODS 31 

solid substratum, serving principally, perhaps, as a means of aeration. 
Wads of pure filter paper, or elder pith which has been carefully 
purified, are both serviceable. 

Certain parasitic, fleshy, or bracket fungi may be grown to advan- 
tage upon dead or normal wood. With a proper regulation of the 
moisture content of the culture chamber fruiting is often readily 
induced upon such media when other substrata fail. 

Siiicate jelly. Silicate jelly as a substitute for gelatin and agar 
was introduced primarily to overcome the difficulties experienced 
in isolating certain organisms in the cultivation of which it is de- 
sirable to avoid organic media. There is, however, a much wider 
use for this preparation. As finer methods are developed it be- 
comes more and more desirable to employ synthesized media for 
a variety of purposes. At best gelatin and agar are of uncertain 
composition, and when, for example, one wishes to determine 
accurately the value of nutrient substances for an organism re- 
quiring solid media, silicate jelly is most serviceable. This material' 
is not difficult to prepare when precautions are taken, and the 
writer has found it practicable in connection with any mineral or 
organic nutrients tested. 

The following materials and special apparatus will be required 
for 500 cc. of the silicate jelly. 

a. I Baume hydrometer for liquids heavier than water, 

b. 200 cc. HCl (sp. g. 1.10° Baume). 

c. 200 cc. sodium silicate (sp. g. 1.09°). 

d. collodion sacks for dialyzing. 

e. 100 cc. nutrient salt solution five times desired strength. 
Stock solutions of b and c may be kept on hand, also of c, \{ 

the same nutrients are to be employed in many experiments. 
Strong hydrochloric acid is diluted with pure distilled water to 
test 1.10° Baume at 15° C. 

Sodium silicate, water glass, is obtainable at a specific gravity 
of about 1.38 to 1.42. Distilled water may be added to this slowly 
until the hydrometer registers 1.09° B. It will usually require 
about seven or eight times as much distilled water as silicate to 
give the specific gravity desired. When required the standardized 
silicate is then added cautiously (dropping rapidly) to the acid, con- 
stantly stirring. 



32 CULTURE MpyrHODS AND TECHNIQUE 

Collodion for the dialyzing sacks is prepared by dissolving five 
grams of guncotton in lOO cc. of a solvent consisting of equal 
parts of absolute alcohol and sulfuric ether. The sacks are prefer- 
ably prepared by the test tube method, and convenient tubes v^^ill 
measure about 30 by 200 mm., with lip. The tubes must be thor- 
oughly cleaned (a final rinsing with ether being desirable) and 
dried. The tube is held in a slanting position and gradually re- 
volved as about 50 cc. of the collodion is slowly poured in, and 
thus an even roll, or coating throughout, with no bubbles, should 
be effected. A second coating is obtained by similarly revolving 
the tube as the surplus collodion is poured out. The tubes are 
then supported upright, mouth downward, and the drip at the lip 
removed. They should then be dried rapidly in a draft at a 
window or preferably under an electric fan, or by exhaust, con- 
stantly revolving each tube meanwhile to maintain even distribution 
of the collodion. When dry, first free the edge of the collodion 
from the tube with a scalpel and then immerse the tube in a vessel 
of water so that as the sack is made free water will pass in between 
the collodion film and the glass, and thus the removal of the film 
may be readily effected. 

The silicate mixture is put in these tubes and they are tied 
securely with a rubber cord and suspended in water over night. 
Running tap water may be commonly employed, but for more 
accurate work it will be necessary to use changes of distilled water. 
The dialyzed liquid should react neutral to litmus and should show 
only a trace of chlorides with silver nitrate. 

The nutrient solution employed may be that mentioned on page 
26, except that the concentration is five times as strong, as pre- 
viously indicated. It is now necessary to boil both the silicate 
preparation and the nutrient solution a few minutes to remove air. 
Then cool down to room temperature, mix and stir, and put into 
the separatory funnel to facilitate pipetting into tubes or other 
vessels to be employed in the work. The silicate in the desired 
vessels is then autoclaved for about fifteen minutes. This should 
insure thorough solidification. Slanting tubes may also be pre- 
pared. It may be necessary for the operator to vary the concen- 
tration of the salts, or to experiment with small quantities when 
using unusual proportions of mineral salts. 



ISOLATION AND PURE-CULTURE METHODS t^t, 

Neutralization of Culture Media 

Neutralization, or properly titration, of most culture media is 
required. It is required in order that definite standards may be 
maintained. In fact, titration is superfluous only in rough work. 
In general, the degree of alkalinity or acidity of the medium may 
affect some of the characteristics of organisms, and, therefore, a 
description of any organism should be made either at a fixed 
standard of alkalinity or acidity, or it should at least be possible 
to reproduce exactly the reaction of the medium employed. The 
colonies of Bacillus prodigiosus and other pigment-forming bac- 
teria are less brilliantly colored when the media are distinctly acid. 
To slight differences of reaction in the substratum fungi ordinarily 
show no marked cultural variations ; yet to greater differences they 
may respond by variations in color, modifications of colony form, 
amount or character of fruiting, etc. 

Most culture media are acid, and sodium carbonate was formerly , 
employed in neutralization. From this, however, carbonic acid is 
liberated, and litmus is temporarily reddened, so that potassium 
hydrate or sodium hydrate is preferable. Moreover, in this titration 
work phenolphthalein, a reliable indicator, has been adopted. It is 
more desirable than litmus, rosolic acid, or other indicators. Litmus 
may be used for rough work, but it is less sensitive to certain acids 
and too variable. In peptone, gelatin, and other organic substances 
there are bodies which are amphoteric, that is, which possess 
both basic and acid properties, the latter predominating. Phenol- 
phthalein is particularly serviceable with respect to those substances. 
Litmus fails to detect such we^k acids ; again, litmus reacts alkaline 
to the dibasic phosphates, while phenolphthalein reacts neutral. 

In titration, the following solutions are desirable : \ per cent 
phenolphthalein in 50 per cent alcohol, as indicator ; gV norrnal 
caustic alkali (preferably sodium hydrate) for the titration ; and 
a normal solution of the caustic alkali for actual neutralization of 
the medium.^ 

1 For practical purposes, a normal solution of sodium hydrate may be prepared 
by dissolving 4.5 grams of c.p., fresh NallO in somewhat less than 100 cc. of 
distilled water, and after it is dissolved make up with water to exactly 100 cc. 
(roughly, this amount makes due allowance for the water and impurities in fresh 
NallO). 



34 CULTURE METHODS AND TECHNIQUE 

Fuller's procedure .lodified may then be a guide ; this is as 
follows : (i) Measure !iy a volumetric pipette or burette 5 cc. of 
the culture medium, and dilute it with distilled water to 50 cc. 
(2) Boil for three minutes in a porcelain dish. (3) Add i cc. of the 
stock solution of the indicator, phenolphthalein, and titrate by add- 
ing the ~}-Q per cent caustic alkali from a burette. Stir constantly, 
and a permanent faint pink coloration will indicate the first appear- 
ance of alkalinity. Those inexperienced in the work should always 
take two or even three samples of the culture liquid and compare 
results as to the amounts of alkali employed. The data are then at 
hand for neutralization or for making the medium correspond to a 
desired reaction. If 6 cc. of the 75L normal alkali, for example, is 
required to bring the two samples to the point of neutralization, 
then the remaining 990 cc, assuming that we employ a liter of 
culture medium, would require practically 100 times 6 cc, or 600 cc. 
of T^Q normal, which is equivalent to 30 cc of normal alkali. Ordi- 
narily, the medium is not neutralized, but is left acid to the extent of 
an omission of 10-15 cc. of normal alkali per liter. In the example 
above, therefore, 15 or 20 cc. of normal alkali would be added. 
A control titration may also be made. 

V. PRESENT METHOD OF ISOLATING ORGANISMS 

In making cultures with a view of isolating, or separating out 
various microscopic organisms, the poured-plate (Petri dish) method 
is now almost exclusively employed. Such cultures may be called 
isolation or separation cultures, the use of the old term dilution 
ailtnrc being less desirable. 

Materials needed. In order to make these isolation cultures, one 
requires nutrient media and apparatus more or less as follows : 

Sterilized Petri dishes, of about 100 mm. diameter; test tubes 
containing about 10 cc. of sterile agar agar ; a few very short test 
tubes without agar ; a platinum needle ; a beaker, or tumbler, with 
some cotton in it, to hold the tubes ; a thermometer ; and some 
boilins: water. The agar in the tubes is melted, either in the steam 
sterilizer or in an open casserole of boiling water with cloth or 
cotton at the bottom. In ordinary culture work, as well as in bac- 
teriological work, three tubes, and consequently three Petri dishes, 
constitute an isolation series. Three tubes of melted agar are 



ISOLATION AND PURE-CULTURE METHODS 



35 



placed in the beaker, which is filled with watc, at from 42^-4 5° C, ; 
and this temperature, which is above the point of solidification of 
agar, should be maintained throughout the period of culture by the 
addition of hot water when necessary. 

The method. In making the cultures the procedure may be as 
follows : Some of the spores or bits of the material from which 
cultures are desired are diffused in a drop of sterile water placed 
in one of the short test tubes (or a flamed slide will suffice). The 
three tubes in the beaker are denoted i, 2, and 3 respectively, and 
may be so marked with a wax pencil. The short tube containing 
the spores and tube No. i are taken between the thumb and index 




WJHT, 



tf-WJ 



%"• 



Fig. 8. Two Dishes from an Isolation Series of a Parasitic Fungus 
(Photograph by Geo. F. Atkinson) 

finger and the index and middle fingers respectively, and held 
almost horizontal, palm upward, the plugs having been previously 
removed and held between the spaces of the remaining fingers. 
The flamed but cold platinum needle, provided with a loop at the 
tip, is taken in the right hand, dipped into the drop of spores, and 
then into the agar of No. i and mixed. This may be repeated 
several times, unless the spores in the drop are very numerous. 
No. I is now placed in the former position of the short tube, and 
No. 2 in the place of No. i. The process is repeated with this 
combination, and, finally, with Nos. 2 and 3 ; the contents of each 
tube is then poured into a corresponding Petri dish upon the top 
of which number, date, and any description desired may be in- 
scribed with the wax pencil. 



J 



6 CULTURE METHODS AND TECHNIQUE 



Frequently, it will be found in practice that in making cultures 
of many parasitic fungi so few spores will be available that they 
may be inserted directly into tube No. i, and it will be necessary 
to pour a few drops of the agar from No. i to No. 2. In fact, 
No. 2 will usually give a very good isolation ; and then No. 3 may 
be used as a No. 2, to which is added a drop of 50 per cent lactic 
acid. Fig. 8 shows an isolation series of GlomcreUa rnfomaadans, 
the bitter rot fungus. 

Elimination of bacteria in isolating fungi. The use of lactic acid 
in culture media is an important aid in eliminating certain trouble- 
some bacteria. In general it may be well to prepare some tubes 
with lactic acid in about the amount above indicated, practically .5 
per cent, so that all tubes used in the isolation series may be thus 
acidulated without danger of contamination. Acidulated media are 
especially valuable when separation cultures must be made by using 
hyphae from a mixed culture, or from any other source which permits 
extraneous organisms to 'come in. In such cases the mycelium 
should be washed as carefully as possible in distilled water, and then 
on being placed in the tubes of liquefied agar, the tubes should be 
vigorously shaken before the contents are poured into the Petri 
dishes. If, however, there is nothing to indicate the relations of 
a fungus to acidity, one isolation series should be made with 
neutral, or very slightly acidulated agar. 

Colony counting. In bacteriological work, and sometimes in 
purely mycological work, it is desirable to make accurate count of 
the number of spores or cells which may have been present in the 
material from which the culture is made. Under such circumstances 
a leveling table must be employed in making the poured plates or 
Petri dish isolation cultures. Plates of glass or other devices, such 
as cardboard charts, especially calibrated for counting colonies will 
also be necessary. 

Study of the isolation colony. In the study and transference 
of the fungi which may appear in isolation cultures, there is a 
rough method which may be pursued, and there is a careful method 
which must be followed if one is to be sure that the life history of 
a particular fungus has been accurately traced. In the first place, 
one may wait until the colonies have appeared, and perhaps until 
growth has been considerably advanced. Then, if isolation is 



ISOLATION AND PURE-CULTURE METHODS 37 

perfect, the species may be more or less readily differentiated, and 
with a sterile needle transfers may be made of each of the one or 
more promising sorts to such media as may have been prepared 
for the purpose. This method suffices, of course, when the desire 
is merely to get cultures of different fungi. When, however, one 
wishes to get the product of a certain kind of spore, it is absolutely 
essential to follow the germination of this spore in the Petri dish, 
to locate germinating spores at a distance from any other organ- 
isms, and then to mark the glass and observe these from day to day 
or to directly remove these isolated spores with some of the sur- 
rounding agar by means of a sterile needle, or scalpel point, to 
tubes of prepared media. In the latter case a considerable number 
of such cultures should be made, and the results may not be taken as 
entirely conclusive unless there is agreement between the cultures 
thus made. When the fungus is one possessing characters by means 
of which it may be readily determined, the problem is not difficult. 

Frequently the spores which are to be located are so small that' 
it will be necessary to remove the cover of the Petri dish, and to 
examine it fearlessly with the agar surface exposed. If carefully 
done, the contaminations resulting are practically negligible. It 
will be necessary to use an objective with a long working distance 
and the ^-inch or i-inch is preferable. A rough examination, 
where the spores are large, may be given by inverting the dish and 
cover, making the examination from the bottom, and then the 
location of spores may be indicated by ink marks. 

Establishing pure cultures: subcultures. The process of trans- 
planting bacteria, spores, or mycelial masses from an isolation cul- 
ture to sterile tubes of prepared media is properly that of establishing 
pure cultures. Frequently it is desirable to make a large number 
of such subcultural transplantings to be used as the stock ailtures 
from which, in future, any necessary series of experiments may 
proceed. 

Under ordinary laboratory conditions, tube cultures may begin to 
dry out in from six weeks to several months, and must therefore be 
renewed or transferred. This consists merely in inoculating fresh 
tubes from the old cultures. A record of such transfers is, for 
physiological purposes at least, important, and may be indicated on 
the label, or in the record book. 



3« 



CULTURE METHODS AND TECHNIQUE 



In making transfers and in examining any tube culture, it is 
well to flame the plug lightly before removal, otherwise particles of 
dust from the surface may fall into the tube and contaminate it. 
The flaming should be momentary, and if the tube is turned so 
that the plugged end is distant from the 
operator, it will be easy to blow out the 
flame. The cork should be removed slowly 
so that there may be no rush of air into the 
tube, thus bringing contaminating dust par- 
ticles. It is needless to say that wherever 
possible tubes should be held horizontally, 
or as nearly so as the contents will permit. 
Storage of cultures. In general, it is not 
well to store tube cultures in a damp place. 
If moisture is constantly in contact with the 
glass, or extends through the cotton plug, 
bacteria will readily enter the tubes. Again, 
under such circumstances fungous spores 
may also germinate, the mycelium may grow 
through the plug, and fruit on the lower side ; 
thus spores will drop into and contaminate 
the culture. When the plugs become wet 
during sterilization, particularly those clos- 
ing flasks of media, the flasks should be 
re-sterilized after the plugs are dry, or after 
fresh plugs are inserted. When placed in 
storage, a paper cone may be placed over a 
few tubes or a crate, or under some circum- 
stances, particularly where it is desirable also 
Fig. 9. Culture OF Pz^c/- to prevent rapid evaporation, one may em- 
ROTus osTKFATus JXcQ. ploy thc rubbcr caps which may be obtained 
(From a Tissue Fragment) ^^^ ^^^^ purpose. A refrigerator is desirable 
whenever cultures are to be maintained fresh for a long period. 
In this case the ice chamber should have no connection with the 
storage chambers. Small compartment cases, such as sectional 
bookcases, are very serviceable for storing cultures away from the 
dust, under laboratory conditions. The culture room (Fig. 14) is 
cleaner when the cultures are stored elsewhere. 



^^^^^H 





ISOLATION AND PURE-CULTURE METHODS 



Sealing cultures. In order to seal the tubes permanently, sealing 
wax may be used after pushing the plug in somewhat below the 
level of the glass. Ordinary beeswax is also effective if a little ster- 
ile paraffin is first poured over the plug and permitted to harden. 
The length of life of a culture 
may sometimes be preserved in 
this way for several years. 

If the cultures are placed in a 
damp place, as in a closed box or 
case, with a surface of water 
evaporating, so as to diminish the 
loss of water from the tubes them- 
selves, it would be well to wipe 
out the case carefully with a dis- 
infectant before use. Where it is 
desired wholly to prevent evapora- 
tion under normal conditions of 
aeration a different method is nec- 
essary. The cultures may be put 
into a clean beaker or tin vessel 
fitted with a zinc screen, or cross 
wired with copper, serving to sep- 
arate the tubes from contact one 
with another. After thoroughly 
flaming the corks the vessel of 
tubes may be placed in a small 
dish or plate of water containing a 
little potassium dichromate and 
the whole covered with a clean 
bell glass. 

Cultures by sporophore frag- 
ments. In his studies upon Aga7'- 
iciis canipcstris the writer ascer- 
tained that fragments of the inner tissue of the hymenophore of 
this fungus placed upon a sterile nutrient medium, such as bean 
pods, sterile compost, soil, etc., would readily develop a vigorous 
mycelium. In order to secure cultures of this particular species 
promptly, it was necessary (i) to use proper sterilization and 




Fig. io. Culture of Polyporus 

SULPHUREUS (V>\5\A..) Fr., A SPECIES 

Tough in Texture. (By Tissue 
Fragment Method) 



40 CULTURE METHODS AND TECHNIQUE 

antiseptic precautions with all material used ; (2) to take fragments 
from a developing (growing) hymenophore and not from one mature 
or decaying ; and (3) to employ a suitable nutrient medium. Under 
such conditions growth is practically invariable (I'igs. 9, 10), unless 
bacteria have previously gained access to the mushroom or the 
culture accidentally becomes contaminated. 

This method, or what was practically the same, has doubtless 
been occasionally resorted to much earlier for obtaining cultures of 
a few fleshy fungi, though practically no attention has been 
bestowed upon the method. The method is, however, capable of 
being used, and has frequently been used, in securing cultures from 
sclerotial stages, and the writer has often employed it in obtaining 
cultures of such stages of certain Sclerotinias. No attempt, how- 
ever, had previously been made to determine its general applica- 
bility. During the past few years this method has been employed 
with a great variety of fungi, — Discomycetes, certain Pyrenomy- 
cetes, and a considerable number of Kasidiomycetes, among which 
were forms widely different as to relationship, texture, and habitat. 
A record was kept of the trials made with sixty-nine species of 
Basidiomycetes, and of these, forty grew promptly on the media 
first employed. The method is especially serviceable in securing 
cultures of forest-tree fungi and other fleshy or woody forms the 
spores of which may germinate only with great difficulty. 



CHAPTER II 

TECHNIQUE OF FIXING, IMBEDDING, AND STAINING 

Chamberlain, C.J. Methods in Plant Histology. (2d ed.) 262 pp. S/Jij^s. 

1905. 
Lee, a. B. Microtomist's Vade Mecum. (6th ed.) 538 pp. 1905. 
Zimmerman, A. (Transl. by J. E. Humphrey.) Botanical Microtechnique. 

296 pp. 1893. 

I. FIXING 

The purpose of a fixing agent is to kill and fix, or render per- 
manent, the structural relations of the cell and the associations of 
cells in tissues. The finer protoplasmic structures are readily dis- 
organized and lost for study, if not carefully fixed by special agents. 
Moreover, adequate fixing is necessary in order to prepare tissues 
to show properly the differential effects which may be gained by 
staining. It is well, therefore, to fix by one or more of the best 
methods such material as may be valuable for minute microscopic 
study. This, however, in no way precludes the desirability of study- 
ing material in a living condition also, — whenever that is possible. 

The material to be preserved should be plunged into the fixing 
solution in a condition as fresh as possible, so that no changes may 
occur subsequent to removal from the natural substratum. Great 
haste is often necessary with delicate fungi in order to avoid dry- 
ing out. It is well always to use an abundance of the fixing liquid. 
With osmic and chroniVJ acids one should often employ as much 
as fifty times the quantity of the liquid as of the material, while 
with alcohol and formalin, fully three times as much liquid as 
material. In all cases, the object, if large, should be cut into pieces 
as small as practicable, in |-inch cubes or less. 

Fixing methods and fixing agents are numerous, and the method 
or agent to be selected will depend upon the kind of study for 
which the material is desired. One method will be applicable when 
histological differentiation is the chief end sought, and when a study 

41 



42 CULTURE METHODS AND TECHNIQUE 

of the fungous hyphae within other plant cells or tissues is desired ; 
while an entirely different method may be essential if the investi- 
gation is to concern itself with more minute cytological details. 

Even when material is to be used for immediate casual study it 
is often necessary to kill and fix it on account of the greater ease 
with which the subsequent operation of staining may be performed. 
In the examination of hyaline filamentous fungi it is unnecessary 
to use any but the simplest methods of fixing on the slide. It has 
been found desirable to treat such hyphse for a minute or two with 
a few drops of a 3 per cent solution of acetic acid. This treatment 
will also generally dispel bubbles of air. The acid should be well 
washed out with water before using basic stains. In the same way 
a 3 per cent solution of potassium hydrate or a weak solution of 
chloral hydrate will often give good results, — the former, particu- 
larly, if the material has suffered any diying out and needs restor- 
ing by the swelling process to which the hydrate is adapted. 

Alcohol. The fixing qualities of alcohol are well known. When 
employed alone it is usually recommended to use either very low 
or very high grades of this agent, and it is serviceable only for 
gross work. Of the lower grades, 15 to 25 per cent are generally 
used, for at this concentration little harm will result from the effects 
of diffusion currents. When the higher grades are used, those 
from 96 per cent to absolute alcohol are preferable, in order to 
effect rapid penetration and fixing. Where the weaker grades are 
employed first, the process is also essentially one of dehydration. 
The size and consistency of the material will determine the length 
of time that the object should be left in the lower grades. It is 
usually left in each lower grade from two to four hours and in each 
higher grade from four to twelve hours. If one begins with 1 5 per 
cent alcohol, the material should subsequently be passed through 
30, 50, and 70 per cent, and for safety in hardening 85 per cent, 
and finally 95 per cent may also be used. Material that is to be 
kept for any length of time should, however, be stored in from 65 
to 75 per cent alcohol, since the higher grades are more apt to ren- 
der it brittle. If material is fixed in from 96 per cent to absolute 
alcohol, it may remain at this concentration for from twenty-four to 
thirty-six hours, and then, if storage is desired, it should be passed 
back to the weaker grade mentioned. 



FIXING, IMHEDDING, AND STAINING 43 

Corrosive sublimate. Corrosive sublimate is always an excellent 
killing and fixing agent for histological staining. It may be used as 
a concentrated aqueous solution, to which, also, the addition of about 
I per cent of acetic acid is often helpful. Whether the material is 
a fleshy sporophore, or a piece of host tissue penetrated by hyphse, 
it should remain in this fixing agent for about twenty-four hours, or 
until the tissue is distinctly white-opaque. The material is washed 
for an hour or two in water, and then carried through the grades of 
alcohol, 30, 50, and 70 per cent, and eventually stored in 65-75 
per cent. If not immediately imbedded, it is well to change the 70 
per cent alcohol several times in order better to remove the subli- 
mate. Sometimes it is necessary to add a little tincture of iodine 
to the alcohol in order to more thoroughly remove the corrosive 
sublimate. If this is done, the liquid should be changed as often 
as it is discolored by the material. It is also claimed that after cor- 
rosive sublimate the material should not long be stored in alcohol, 
as such material will readily become brittle. 

It is often preferable with fungous tissue to use a concentrated 
solution of the sublimate in 96 per cent alcohol, to which it may 
also be well to add i per cent acetic acid. This mixture penetrates 
more readily and is more valuable for cytological work than the aque- 
ous solution. Objects thus fixed are transferred after from a few 
minutes to twenty-four hours to lower grades of alcohol, and wash- 
ing may be effected by a few changes at the grade used for storage. 

At laboratory temperatures mercuric chloride is soluble in water 
to the extent of about 5 to 6 per cent, and it is much more soluble 
in alcohol. If it is desired to use stronger solutions of the mer- 
curic salt, it will be necessary to add to the solution some chloride, 
such as sodium or ammonium. As will be seen later, both the car- 
mine and anilin stains may be used after corrosive sublimate, and 
the mixtures of this agent are especially good for fixing parts of 
any of the fleshy fungi. 

Chromic acid and chrom-acetic acid. Solutions of chromic acid 
from .5 to I per cent are sometimes used for fixing fungous mate- 
rial ; but in general it is so much less valuable alone than in 
combination with acetic acid of less or equal strength that the com- 
bination should be employed. Wash and dehydrate as for the next 
fixing agent. 



44 CULTURE METHODS AND TECHNIQUE 

Chrom-osmo-acetic acid. This mixture, commonly known as 
Flemming's solution, is very satisfactory for cytological work with 
plant tissues. It is particularly desirable as a fixing agent to pre- 
cede the triple stain, also iron haematoxylin ; and these are two of 
the best cytological stains. As commonly employed, the Flemming 
solution varies greatly in strength. The weaker solution is ordina- 
rily to be recommended. This should include as an aqueous 
solution chromic acid from 4 to i- per cent, osmic acid J^ per cent, 
acetic acid -Jq per cent. It is possible, however, to employ the 
solution at least twice as strong as the formula given, and it is 
convenient to make stock solutions of each substance rather than 
to make up at one time a large quantity of the fixing fluid. More- 
over, the stock solutions mentioned may be so prepared as to serve 
for any strength of the Flemming which may be required. Stock 
solutions should be as follows : 

Chromic acid i per cent 

Osmic acid i per cent 

Acetic acid i per cent 

In order to prepare the weaker fluid, the following quantities 
will be required : 

I per cent chromic acid ... 25 cc. 

I per cent osmic acid . . . 10 cc. 

I per cent acetic acid . . . 10 cc. 

Water 55 cc. 

Stock solutions are very desirable on account of the fact that the 
Flemming does not keep well, especially when constantly opened 
for use. Any solution containing osmic acid turns black promptly 
upon contact with certain organic material or dust. This effect is 
facilitated by light, although light alone is noninjurious. It is 
advisable, however, to store the osmic acid in a brown bottle, or to 
keep it from the direct sunlight. 

Ordinarily, material should be left in this mixture from twenty- 
four to forty-eight hours, and it should then be washed in running 
water two to four hours and finally passed through the different 
grades of alcohol beginning at 15 or 30 per cent until the desired 
storage grade is reached, or until the material is thoroughly dehy- 
drated, if it is to be immediately imbedded. After the use of the 
Flemming mixture, however, it is often necessary to decolorize the 



FIXING, IMBEDDING, AND STAINING 45 

material. The decolorization is best effected when the material is 
in 70 per cent alcohol, and during the dehydration process. The 
simplest method is to add to three parts of 95 per cent alcohol one 
part of hydrogen peroxide and allow the material to stand in this 
mixture from twelve to twenty-four hours. It seems to be less 
injurious to decolorize in mass than eventually to decolorize the 
sections on the slide, just prior to staining. 

Alcoholic mercuro-nitric acid solution. This fluid should be 
more generally employed with the fungi, since it penetrates well, 
and may be advantageously followed by hcematoxylin, anilin, and 
carmine stains. Gelatinous masses of spores remain intact fairly well 
in this. About 300 cc. may be conveniently made up as follows : 



Water 

96 per cent alcohol . 
Glacial acetic acid . 
Nitric acid 
Corrosive sublimate 



270 cc. 

30 cc. 

2 cc. 

5 cc. 

10 grams 



Material should remain in this agent from one to six hours, then 
it may be passed through grades of alcohol to 70 per cent, where 
several changes of the liquid should be made. 

I have not found picric acid, or combinations of this with mer- 
curic chloride and other agents, satisfactory for work with the fungi. 

Formalin is, of course, a good general preserving liquid, but it is 
not practicable when imbedding methods may afterwards be 
employed. 

II. THE PARAFFIN PROCESS: INFILTRATION AND 
IMBEDDING 

Material which is to be sectioned by means of the microtome is 
now far more commonly imbedded in paraffin than in celloidin or 
collodion. Some chief advantages claimed for the paraffin method 
are : ( i ) better penetration of the imbedding substance, permitting 
more uniform and thinner sections ; {2) facility in cutting, together 
with ease of preserving the sections in serial order ; (3) convenience 
of the paraffin ribbon in the further processes involved. 

Assuming that the substance which is to be imbedded is stored 
in alcohol, it becomes necessary, as the first step, to dehydrate 
thoroughly by treating with 90 per cent alcohol during about twelve 



46 CULTURE METHODS AND TECHNIQUE 

hours, and then with absolute alcohol. It is desirable to change the 
absolute alcohol once, permitting the material to remain each time 
from four to six hours. 

The infiltration methods, that is, methods by which the penetra- 
tion of paraffin into the tissues and cells is effected, are various, and 
biologists do not agree as to which is most practicable. The chief 
difference lies in the nature of the solvent employed to precede the 
paraffin. After having tried for years chloroform, xylol, and cedar 
oil in turn, it is preferred with the majority of tissues to employ 
the chloroform method, — a method at once simple and sure. It is 
as follows : 

The chloroform infiltration method. The material from absolute 
alcohol is put into a mixture of equal volumes of absolute alcohol 
and chloroform. It is permitted to remain in this mixture for from 
twelve to twenty-four hours, and then pure chloroform is sub- 
stituted. In the pure chloroform readily penetrable tissues will soon 
sink and will be thoroughly penetrated within twenty-four hours. 
Many tissues will require two days, and two days may be most 
desirable. At the end of this period, whether the tissue is sunken 
or not, it is poured out into an open dish (small porcelain vessels 
2 or 3 centimeters broad and deep being very desirable), and into 
this dish is cut more than enough hard paraffin (53° to 54° C.) 
finally to cover the material with paraffin alone, or, better, suffi- 
cient in which finally to imbed the material. These dishes are then 
put into the oven at 55° to 56° C. and the chloroform evaporates 
within a day or two. If stirred once or twice, it will evaporate more 
promptly, and the material is then in excellent condition to be 
imbedded in the papers or special imbedding trays commonly used. 
Paraffin used in this process, if the chloroform has all evaporated, 
is excellent from the standpoint of viscosity, and consequently it 
will cut more evenly than fresh paraffin. 

Cedar oil and xylol infiltration. Some prefer to use cedar oil as 
a solvent with the paraffin. That method, however, is somewhat 
more taxing and seldom to be recommended. The cedar oil is 
more difficult to remove from the tissues, and I have found it 
desirable only in cases where the material is exceptionally brittle. 
When cedar oil is employed, it seems desirable to pass from 
absolute alcohol to a mixture of cedar oil and alcohol, the tissues 



FIXING, IMBEDDING, AND STAINING 



47 



sinking from the alcohol into the cedar oil, and this indicates the 
time when the mixture may be replaced by pure cedar oil. After 
remaining in the cedar oil for from twelve to twenty-four hours soft 
paraffin may be added. In from twelve to twenty-four hours hard 
paraffin may be used, and after a similar period the material may 
be imbedded in trays in fresh paraffin. It is desirable in this proc- 
ess to have the material held in little wire-meshed ladles, and thus 
the change from one grade of infiltrating agent to another is effected 
by a transfer of the ladle from one vessel to another. In each case 
the ladle is thrust into the liquid sufficiently to cover the bowl and 
material. The cedar oil is then more readily displaced, sinking to 




Fig. II. A Desirable Outfit for Sectioning and Staining 



the bottom, and there are fewer difficulties in sectioning on account 
of electrification, which is intensified by the presence of oil. 

Xylol is also employed in infiltration, but with some tissues there 
seems to be a peculiar optical effect produced, and it has no pecu- 
liar advantages for this purpose. 

Sectioning. When the objects are imbedded they should be so 
disposed that each, or each group, is far enough from those adjacent 
to permit of its being readily cut out and attached to the object 
carrier. When melted to the carrier careful orientation is given. 
Sectioning is a simple operation with material properly infiltrated, 
with a sharp razor or microtome blade, and with the laboratory at 
living-room temperature. Very tough or carbonaceous fungi will 
never yield satisfactory sections by the paraffin method, but the 
great majority of the parasitic fungi may be thus treated. There 



48 CULTURE METHODS AND TECHNIQUE 

is a tendency to make the sections too thin when this method is 
employed. Some thin sections will usually be required, but for such 
studies as the distribution of the fungus in the host, and the forms 
and relations of fruiting organs, thicker sections are preferable. 

Attaching sections. Since the paraffin method is here presented 
in some detail, a few indications with reference to fixing sections to 
the slide and the further manipulation of the material will be 
requisite. A inuuite drop of ^^% albumen preparation ^ is first 
rubbed over that portion of the slide to which the sections are to 
be affixed. Add a few drops of water from a pipette, arrange the 
sections or ribbon exactly as may be desired on the slide, allowing 
for expansion to their normal size, and place the slide immediately 
in the paraffin oven, that is, at a temperature which will just melt 
the paraffin (Strasburger's method). In two hours the slides will 
be ready for removal and for the subsequent processes. The method 
mentioned is simpler and better than the one in which more 
water is added when the sections arc laid on the slide, the slide 
warmed over a flame until the sections spread out, the water drained 
off, and finally the slides set aside from four to twenty-four hours 
to dry in a warm place. In either case, when the slides are 
thoroughly free of moisture, they are passed into the xylol for a 
few minutes, then into absolute alcohol, and to such other grades 
as are necessary prior to staining. In all of these processes Cop- 
lin's staining jars or other similar vessels are desirable. Care 
should always be taken to remove every trace of paraffin before 
proceeding further. 

III. STAINING 

Filamentous fungi. It is often necessary to employ staining 
methods in an examination of hyaline filamentous fungi, even if 
the observation is merely for the provisional determination of the 
fungus at hand. This is particularly true in an examination of 
certain mold or hyphomycetous fungi. Such fungi, and particu- 
larly the aerial parts of such fungi, should be well teased out in a 
drop of weak acetic acid, or sodium hydrate in lo to 20 per cent 
alcohol, on the slide. This killing agent is drained off by means 
of filter paper, the preparation washed, and then it may be stained 

^ Egg albumen, 50 cc. ; glycerin, 5 cc. ; and salicylate of soda, \ gram. 



FIXING, IMBEDDING, AND STAINING 49 

with a solution of eosin. A % per cent aqueous solution will suffice, 
but alum eosin (.V per cent alum) is even better. Unless the object 
is first killed, as by being treated with acid, the stain will very 
readily disappear, or become indistinct, when mounted in glycerin 
or in glycerin jelly. A l per cent solution of fuchsin may also be 
used. Hyaline fungi to be preserved as glycerin preparations 
should always be stained, otherwise the fungous outlines will in 
time become very indistinct. 

Many of the fungi may be carefully studied for purposes of 
identification and for a knowledge of their general structure with- 
out the use of stains and staining methods. To this class belong 
practically all of the filamentous fungi which are not hyaline, that 
is, those which are flavous, olivaceous, brown, or otherwise colored 
in such a way that the outlines of cell walls show distinctly when 
mounted in water, glycerin, glycerin jelly, etc. The most delicate 
fungi are those which necessitate the use of stains, such as many 
members of the Miicoracece, Sap7'oleg7iiacecB, Peronosporace(E, and 
other related orders, as well as many mucedinous Hyphomycetes. 

It is usually recommended to make up concentrated alcoholic 
solutions of eosin and fuchsin as stock solutions. Then, as desired, 
weaker stains may be prepared from the above by dilution with 
water, the latter, of any strength desired, being kept conveniently 
in dropper bottles. The staining process is very simple and con- 
sists merely in adding a drop or two of the stain to the preparation 
on the slide, then washing it off with water when the desired effect 
has been produced. A drop or two of low-grade or acidulated alco- 
hol will usually remove any overstaining. 

It has been ascertained that those fungi which are stained only 
with difficulty by this process are much more readily stained if an 
acid or an alkaline solution of the stain is employed. Carbol fuchsin 
is one of the recognized strong stains of this class. This may con- 
veniently consist of a .5 per cent aqueous solution of carbolic acid, 
to which is added sufficient of the concentrated fuchsin stock 
solution to make a strong stain. 

Fleshy fungi and tissues. Staining processes such as have been 
already described are very simple when compared with most of 
those which must be resorted to when the material consists of a 
fungous tissue, or of other tissue penetrated by a fungus. Loose, 



50 CULTURE METHODS AND TECHNIQUE 

readily penetrable tissues may be stained in mass with a ground 
stain, but in general it is preferable to stain sections on the slide. 
Material of the fleshy fungi more often lends itself to mass stain- 
ing, and this process becomes particularly desirable, moreover, 
when carmine stains are advised. The carmine stains are most 
important if the material has been fixed in sublimate mixtures. 

A successful method of staining fleshy fungi for histological 
differentiation has been used by Burt as follows : — Alcoholic 
material is stained /;/ toto twenty-four hours in Mayer's alcoholic 
paracarmine. When the sections have been mounted on the slide 
and dehydrated, they are stained for about five minutes in an 
aqueous solution of fairly strong safranin, and finally washed in 
water, previous to mounting in water and glycerin. With tissues 
fixed in sublimate mixtures, the Ehrlich-Biondi-Heidenhain stain 
has also been found to give effective histological differentiation. 
This strain should be obtained ready-mixed from Griibler & Co. 
To lOO cc. of 0.4 per cent solution of this mixture must then be 
added 7 cc. of a |- per cent acid fuchsin solution. This stain 
gives some nuclear differentiation, but it cannot by any means 
be called a successful nuclear stain. Only small quantities of this 
stain should be combined with the fuchsin at one time, since its 
keeping qualities are not good. 

A double stain of any standard haematoxylin followed by 
erythrosin eosin or orange G is sometimes to be recommended 
when material is fixed in alcohol ; but, in general, many haema- 
toxylin stains are not so valuable for work with the fungi as with 
the higher plants. Magdala or Congo red may be followed by an 
anilin blue or green to advantage. A stain of any solution of eosin 
or carmine followed by a counter stain of nigrosin is often of value. 
In cytological work more than in any other kind, it is necessary 
to bear in mind the nature of the fixing agent in deciding upon 
an effective stain. After sublimate fixing, one of the most success- 
ful methods of staining on the slide for the differentiation of cyto- 
plasmic and nuclear structures is one apparently first published by 
Wager. It is a cumbrous and complicated process in print, but is 
much simpler in practice. As I have used this stain, it is a slight 
modification and simplification of Wager's process. The principal 
solutions needed are : 



FIXING, IMBEDDING, AND STAINING 51 

1 . A 50 per cent solution of alcohol containing a trace of nigrosin and acetic 
acid. 

2. Mayer's alcoholic paracarmine. 

3. 5 per cent glacial acetic acid in 50 per cent alcohol, to which is added 
sufficient nigrosin to make it bluish black in the bottle. 

4. 50 per cent alcohol strongly acidulated with acetic acid. 

The sections on the shde are mordanted for a few minutes in 
I. They are then somewhat understained in sokition 2, the 
superfluous stain washed off in 50 per cent alcohol, and the slide 
placed in 3. In this last it remains until examination shows it to 
be slightly overstained. It is then washed and decolorized to the 
desired degree in the 50 per cent alcohol strongly acidulated with 
acetic acid (4). 

Mayer's alcoholic paracarmine, used in this connection, is made 
by using carminic acid i gram, chloride of ammonium 0.3 grams, 
chloride of calcium 4 grams, and 100 cc. of 70 per cent alcohol. 
Dissolve the carminic acid by heat if desired for immediate use, 
then allow it to settle, and filter. 

Flcmiimig triple stain. When material has been fixed in chromic 
acid solutions, particularly in the Flemming chrom-osmo-acetic, then 
the Flemming triple stain is one of the two most valuable with the 
fungi, as with nearly all other plant tissues similarly fixed. This 
stain requires safranin, gentian violet, and orange. The usual 
method is to stain on the slide for several hours to a day in a 
strong alcoholic solution of safranin, rinse in 95 per cent alcohol 
until very little color remains, stain for a few minutes to several 
hours in gentian violet, wash for a very short time in water, and 
plunge into a strong solution of orange G for a few seconds. The 
slide is then treated with absolute alcohol in order to wash out the 
surplus gentian. Differentiation is effected by treatment with clove 
oil or with clove oil first, and finally with xylol for fixing, before 
being mounted in damar balsam. Almost any safranin stain may 
be used in this combination, but it will often be found that the 
safranin may be entirely omitted with advantage. By this means 
the process is also greatly shortened. Perhaps the best gentian 
violet which may be used in this process is that of Ehrlich, con- 
sisting of : 

Gentian violet . . i part Anilin oil ... . 3 parts 
Alcohol .... 15 parts Water 80 parts 



52 CULTURE METHODS AND TECHNIQUE 

The method of procedure with the gentian will depend on whether 
a chromatic or a kinoplasmic stain is desired. In the first case a 
short immersion in a strong stain will give best results, and in the 
latter case it is often well to use only a few drops of the gentian 
to a tumbler of water. The orange acts rapidly upon well-fixed 
structures, and often an immersion of a few seconds will suffice. 
Clove oil washes out the gentian somewhat in clearing, but berga- 
mot oil does not have this effect, and serves rather to fix the stain, 
so that it may sometimes be necessary to dash the slide with berga- 
mot oil before differentiating with clove oil. In every case, how- 
ever, considerable experimentation is necessary for the proper 
handling of this stain. 

Iron hcentatoxylin. Where the safranin-gentian-orange is in- 
effective, iron haematoxylin will often give excellent results. With 
this process the sections are immersed from one to several hours 
in about a 3 per cent solution of iron alum (ammonia-sulphate of 
iron). They are next washed well in water and then stained in a 
0.5 per cent aqueous solution of haematoxylin. The latter is allowed 
to act until a considerable overstaining has resulted. The slide is 
then washed and again put into the iron solution until the desired 
differentiation shall have resulted. It is then dehydrated, etc., as 
usual. Iron haematoxylin will give some brilliant results when the 
Flemming combination is ineffective. It is usually necessary to 
considerably overstain the preparations and then to wash out 
strongly in the alum solution if chromatin differentiation is 
desired. It is sometimes well to follow this treatment with a 
slight ground stain of orange G. 

After Merkel's solution good results have been obtained by 
Harper with a double stain of acid fuchsin and iodine green. The 
same stain has also been found useful after corrosive sublimate by 
Wager in his studies upon the cytology of the yeasts. 

Bacteria. Only a few general directions may be given dealing 
with some of the ordinary methods now employed for the staining 
of the bacteria. The concentrated alcoholic solutions mentioned 
for the fungi are used, and, in addition, a similar solution of 
gentian violet. These solutions are sometimes made of definite pro- 
portion, standard strengths being i gram of the stain to 10 cc. of 
95 per cent alcohol. These solutions are diluted for use, just as with 



FIXING, IMBEDDING, AND STAINING 53 

the fungi. Carbol fuchsin is also largely employed in the staining 
of bacteria. The alkaline stain most widely employed is perhaps 
Loefifler's alkaline methylene blue. This solution consists of: 

Alcoholic solution methylene blue 30 cc. 

I per cent solution potassium hydrate .... i cc. 

Distilled water 100 cc. 

Other excellent stains are Ehrlich's anilin-water fuchsin and gentian 
violet. These are made by adding to 10 cc. of distilled water an 
excess of anilin water ; this being shaken until no more will dis- 
solve, and then filtered. To such solutions are then added i cc. 
of the saturated solution of gentian violet or of fuchsin. 

In order to stain effectively the flagella of bacteria rather com- 
plex methods are necessary. No method is satisfactory unless 
every precaution is taken to have (i) the cover slips thoroughly 
clean ; (2) the organism from a young (twelve to twenty hours), 
vigorous culture, on a suitable medium ; and (3) the bacteria' 
evenly and thinly disposed upon the slip. Where experience has 
not taught one to what extent to dilute a loop of bacteria for the 
best staining effects, it is well to arrange the covers in series of 
from four to five. Place a minute drop of water upon each slip, 
then diffuse the bacteria from the culture in the first drop, and 
with a loop from the first drop pass to the second, third, etc., in 
turn, first diffusing the contents of the loop, then sweeping the 
needle across the cover and passing to the next. These are dried 
and fixed to the slip as previously indicated. 

There are several important methods of staining flagella. Loeffler's 
method, or some modification of it, is frequently employed. This, 
like most flagella methods, involves two chief operations, viz., mor- 
danting and staining. The mordant consists of : 

20 per cent tannic acid solution 10 cc. 

Saturated solution of ferrous sulfate .... 5 cc. 
Saturated solution of fuchsin, aq. or alcoholic . . i cc. 

This mordant may be generally used as above, or it may be necessary 
to add an acid (in the case of certain alkali-producing organisms) 
or an alkali (certain acid-producing organisms), according to Loeflier, 
this being done by adding to the mordant a fractional percentage 
of weak stock solutions of a caustic alkali and an acid. 



54 CULTURE METHODS AND TECHNIQUE 

A few drops of the mordant are placed upon each shp (pref- 
erably supported by the cover slip forceps). The slip is held 
cautiously high above a small flame until vaporization begins ; the 
mordant is then washed off with water, followed by alcohol ; finally 
the preparations are stained in anilin-water fuchsin, washed, dried, 
and mounted in balsam. 

The modification of the above stain by Lowitz is strongly rec- 
ommended. This consists in substituting copper sulfate for the 
iron salt. The preparations are generally mordanted from thirty 
seconds to three minutes and washed. They may then be stained 
in the anilin-gentian violet of Ehrlich and the surplus stain washed 
out in water, 50 per cent alcohol, or acidulated alcohol. Freshly 
prepared solutions both of the mordant and of the stain should be 
employed. 



PART II 

PHYSIOLOGICAL RELATIONS 

CHAPTER HI 

GERMINATION STUDIES 

Clark, J. F. On the Toxic Effect of Deleterious Agents on the Germination 

and Development of Certain Filamentous Fungi. Bot. Gaz. 28 : 289- 

327, 378-404. 1899. 
DuGGAR, B. M. Physiological Studies with Reference to the Germination of 

Certain Fungous Spores. Bot. Gaz. 31: 38-66. 1901. 
Ferguson, M. C. Germination of the Spores of Agaricus campestris and 

Other Basidiomycetous Fungi. Bur. Plant Ind. U. S. Dept. Agl. Built. 

16: 1-43. ph. 1-3. 1902. 

Requirements for germination. With regard to their require- 
ments for germination, the spores of fungi show very marked 
differences. It may be possible to group the fungi in three 
categories, based upon their minimum requirements, although 
it is very probable that the Hmitations of these classes may 
not be fixed with any degree of definiteness. These classes are 
as follows : 

1 . Those which may germinate in moist air or in water. 

2. Those which require a nutrient solution, 

3. Those which require a special stimulus. 

Where the spore germinates in moist air or in distilled water it is 
merely the absorption of water, under external conditions favorable 
for growth, which suffices to give the necessary incitation. In other 
words, the spore is then undoubtedly provided with its own food 
material. Many parasitic fungi evidently belong to this class. No 
nutrient substance is known to enhance the germination of spores 
of the Uredinales, Peronosporales, and some other obligate parasites. 
This statement is necessarily put in this form on account of the 
fact that many observers have employed ordinary tap water in their 

55 



56 PHYSIOLOGICAL RELATIONS 

experiments. Conidia, aecidiospores, and uredospores ordinarily 
germinate best immediately after maturity ; but oospores and 
teleutospores generally require a period of rest. It is certain that 
a few saprophytic fungi may also germinate in distilled water. 
This is true of (Edoccphahnn albidum, some species of Botrytis, 
and certain hyaline-spored Basidiomycetes. 

In general, the saprophytic fungi seem to require a nutrient 
medium for germination ; and the percentage of germination de- 
pends largely upon the direct food value of the medium, the per- 
fect food affording the best germination. This is particularly true 
for Penicillium, Aspergillus, certain Mucoraceae, and probably 
many other fungi. Moreover, plant pathologists generally recog- 
nize that most of the imperfect or ascomycetous parasitic fungi 
germinate most readily in nutrient solutions. Certain of these 
fungi germinate best in infusions or decoctions of the host plant. 
Excellent germination may occur in a solution containing a single 
nutrient, as in sugar solution, glycerin, a nutrient salt, etc. Such 
cases may, perhaps, justly be classed among food stimuli. 

It is known that many parasitic phanerogams require a special 
stimulus of the host plant before germination may be incited, and it 
is reasonable to believe that similar instances will be found among 
the fungi. According to De Bary, the hoof and feather fungus, 
Onygena cor^nna, requires such a stimulus. Very little special work 
has been done along this line of inquiry, and interesting results 
may be expected, particularly with species which have thus far 
proved refractory under the usual methods of culture. Miss Fergu- 
son has determined that while Agaricus campcstris may germinate 
more or less erratically in many nutrient media, or with special stim- 
uli, the best and most constant germination yet secured is obtained 
by placing in the culture drop a few strands of the growing hyphas 
of the same fungus. In such cases, as a rule, a germ tube of a length 
not greatly exceeding the diameter of the spore is emitted, but no 
further growth results unless the spores are transferred. This 
stimulation occurs whether the medium employed is a nutrient 
solution or distilled water. These results I have been able to con- 
firm repeatedly. Moreover, I have found that a similar stimulus 
to germination is afforded by placing in the culture drop a frag- 
ment of the fresh tissue of the sporophore. The latter is able to 



GERMINATION STUDIES 57 

develop a new growth upon which the stimulus, for the most 
part, depends. In some instanced germination has been secured 
in an infusion (implying no cooking or sterilization) of the fresh 
tissue. 

It has been found by Eriksson that short and sudden cooling 
has a marked influence to increase the amount of germination in 
the aecidiospores of the wheat rust, so that a stimulus from the 
temperature relation may be inferred. It may be well further to 
inquire if the "resting" period is essential to the germination of 
certain spores. If resting spores might be forced into germina- 
tion by special stimulation, pathological work might be greatly 
facilitated, and material made available for valuable cytological 
studies. 

Methods of study. Studies in the germination of fungous 
spores in solutions, or in water, are best made by the use of the 
hanging-drop culture method generally inappropriately called the 
Van Tieghem cell. This method consists essentially in sowing 
the spores in a drop of the desired medium on a cover glass 
and then inverting this cover glass over a glass ring cemented 
to a glass slip. The old method of using slides with drop de- 
pressions in them is not so satisfactory, and cardboard rings 
give unreliable results. It is necessary to give the details of the 
method referred to at considerable length. For ordinary pur- 
poses I have found it desirable to use glass cylinders of 15-18 
mm. internal diameter and 9-10 mm, high, preferably 16x10 
mm. Xylonite rings produce products in the cell which may be 
injurious. Rings of such size as indicated provide an abundance 
of oxygen, and with them the 18 or 20 mm. square and round 
covers are available. Round covers are preferred, since fewer acci- 
dents occur in using them. Slips and rings must first be carefully 
cleaned by the process previously mentioned. In some very deli- 
cate experiments, where even the vapor from vaseline should be 
avoided, rings may be placed in a Petri dish provided with filter 
paper in which holes are cut for their insertion (Fig. 13,^). 

The rings are cemented to the slips by means of beeswax alone, 
or beeswax with the addition of a small amount of vaseline. ^ For 

1 Waterproof permanent cements may also be employed, but they are not 
generally satisfactory. 



58 



PHYSIOLOGICAL RELATIONS 



very careful work purified beeswax and white vaseline should be 
used. As a matter of convenience, two rings are usually cemented 
to the same slip. To make the cells, the wax is kept melted, the 
slide is slightly heated in the flame, and by means of the forceps 

the ring is passed through the 
fiame, after which one edge 
is dipped lightly into the 
melted wax, then cjuickly 
placed upon the slip. If the 
wax is too hot, it will be nec- 
essary to touch the ring sev- 
eral times to the melted wax, 
then raise it high enough to 
cool somewhat. When the 
wax is cool the free edge of 
the cylinder is provided with 
a ring of vaseline by invert- 
ing the cell over a slip, or 
shallow watch crystal, upon 
which there is spread a thin 
layer of melted vaseline (Fig. 
12). The cell should be 
momentarily held in this inverted position, or rested in this position 
on a rack, in order that the ring of vaseline will have some depth. 
By means of the vaseline ring the cover is, at the proper time, 
cemented firmly to the glass cylinder. If the temperature at which 
the cultures are to be incubated differs considerably from that at 
which the cells are made, it has been found well to m'ake with 
the back of a scalpel a small nick in the vaseline ring, through 
which nick the expanding air may pass when the cultures are 
placed in the thermostat, or culture incubator. Afterwards they 
may be permanently sealed by slight pressure with scalpel or 
needle. A drop of the culture fluid to be used is placed on each 
cover glass, and about half a dozen drops of the same fluid are 
placed in the bottom of the cell. A small glass rod is the- only 
satisfactory dropper for the first-mentioned work. The drops are 
inoculated with a few spores by means of a platinum needle, 
massing or bunching of the spores being prevented as much as 




Fig. 12. Stand and Dish for Beeswax 



GERMINATION STUDIES 



59 




Fig. 13. Rings for Drop Cultures 
(7, cemented to slide ; /', in Petri dish with filter paper 



possible. It is sometimes desirable to distribute the spores pre- 
viously in a drop or small quantity of water, otherwise one may 
get too many in the culture drop. The covers are then inverted 
over the glass ring and pressed down so as to leave only one 
minute unsealed area. 

It is an unwise and an inaccurate plan to use in the bottom of 
the cell any other liquid than that used in the culture drop. This 
must be so in order that 
there may be no differ- 
ences of vapor pressure, 
and consequently no evap- 
oration from drop to liquid 
below, cr vice versa. For 
instance, it would be man- 
ifestly absurd to test ger- 
mination in a drop of, say, 
5 per cent alcohol above if 
there were only pure water below. If there is danger of contami- 
nation below, and consequent interception of the light, thorough 
sterilization must be given beforehand. If the drop cultures are 
made as soon as the slides are prepared, sterilization should not 
be necessary, since all parts are flamed. Sterilization may be 
given at any time, however, previous to the ringing with vase- 
line. It is usually sufficient to sterilize the cells in a dry oven at 
a temperature of from 110° to 115° C. This temperature melts 
the wax, but if the slides are level, there is no danger that the 
cells will slip. A temperature much higher is not to be recom- 
mended. Another convenient method of sterilization is by means 
of formalin. The cells are filled with a solution of from 3 to 5 
per cent formalin, and this is allowed to stand for half an hour ; 
then on being rinsed with distilled water, again filled with the 
water, and left for ten minutes they will be found sterile. The 
cells should then be inverted and dried before the ringing with 
vaseline is effected. By this process some cells will become dis- 
connected ; but if the cementing has been well done, this is a 
matter of small importance. 

Since it will often be found desirable to invert the slides and 
cells to prevent contamination while awaiting use, the work should be 



6o 



PHYSIOLOGICAL RELATIONS 



done in a culture room (Fig. 14), and tin racks should be provided. 
Miss Ferguson ^ has devised a convenient stand for holding slides 
in cell culture work ; and since in many laboratories where infection 
experiments are made, or where physiological work is done, large 
numbers of these cells may be used, this stand becomes a very use- 
ful device. It has been 
described as follows : 

A stand for hanging-drop 

cultures. A stand for support- 
ing slides when one is using 
the Van Tieghem cells should 
be made of such material and 
in such a way that it will 
neither burn, warp, nor melt 
upon being heated, for it is 
often desirable to sterilize the 
cells before making up the 
cultures. It should also com- 
bine economy of space with 
ease of manipulation. All 
these points are characteristic 
of the little piece of apparatus 
which I have used. . . . 

This stand consists, as will 
be seen from the photographs 
. . . , of a series of trays 
placed one above the other. 
Each tray was made from a 
single piece of tin without the 
use of solder. The tin meas- 
ured 13^ by 3I inches after it 
was hemmed. This was folded 
on the sides just as one folds 
a piece of paper in making the boxes described by Lee (1896) for imbedding 
material in paraffin. A strip 1 1 inches wide along both ends and on one side 
was bent up at right angles to the rest, so that a bo.K open at the top and along 
one side was formed, which measured 1 1 by 2| inches on the bottom. The 
double, triangular, carlike projections formed at the two corners were folded 
along the back and secured by means of rivets. The tin was then cut, or 
slashed, | of an inch deep, i inch distant from either corner on the back. 
Similar cuts were also made at the corners, and three equally distant from 
each other and from the outer edges were made on either end. The segment 







lUinyHni 


^S^^B ^HHlf^OHp^p^-^^l 


HB^B^Hl^^^if^ 


^^^^^^^^^^^^■^^^^^^^^^^■' ' fi \ S^^^HI^^^^^^^^^HI m 




^^^^^H^^v^^^M^^^Hf 



Fig. 14. A Small Culture R(jom, Conven- 
ient AND Easily Cleaned 



1 Fergusor, M. C. Bureau Plant Industry, Built. 16, /. <■. 



GERMINATION STUDIES 6 1 

of tin along the middle of the back and those next to the free outer segments 
on the ends were folded in until parallel with the bottom. These act as a shelf 
on which to rest the next higher tray. The outer and innermost segments at 
both ends were bent outward, forming projections which are very useful in 
lifting the trays. The second segment from the corner at either end was bent 
out at right angles to the side, and then the outer portion of it was again turned 
up until it was parallel with the position which it formerly occupied. These, with 
the segments at both corners along the back, which were left erect, prevent the 
next higher tray from slipping or sliding. It was found desirable to cut the 
bottoms of the trays out, since the rapid absorption of heat by the tin has a tend- 
ency to increase the condensation moisture on the cover glasses. 

P'or convenience in use it is necessary that trays be about \ inch narrower 
than the slides are long. Unfortunately, the slides thus extending over the 
edges of the pans are very easily struck, and the cultures thereby endangered 
when one is putting other material into or taking it out of the thermostat. To 
guard against such accident, as well as for greater ease in carrying, a bottom 
tray was made j inch wider than the others, and with a back 51 inches high. 
This tray had five segments cut at each end instead of four, and these were 
turned the same as in the other trays, except that the outermost one was 
bent in to give greater stability. Shelves were made along the back by cut- 
ting and folding in the tin at these points. The windows thus formed give 
free circulation of air. These windows, each 2| inches long and i inch deep, 
were so cut that if the pieces of tin freed along three sides had been bent 
straight inward, they would have formed shelves 1 inch higher than those at 
the ends. But they were doubled in close against the back for an inch, and 
then turned out until they stood parallel with the bottom of the tray. This 
gives a little back at the points where the windows occur, and prevents any 
cultures on the second tray from slipping through these open spaces. For 
convenience in handling, the bottom was n'ot cut from this first tray as from 
the others, and it may be used for a support for cultures or not, at the discre- 
tion of the operator. 

The trays were all made of the same size. ' Five trays besides the bottom one 
constitute a " set " as we have used them. Each such set holds 1 20 cultures, 
and occupies only 36 square inches of space in the thermostat. The trays may, 
of course, be made of any length or of any height, the dimensions given are 
those best suited to the thermostat which we have used. When all the trays 
have been filled in making up a set of cultures the five upper ones are lifted 
together and so placed on the lowest pan that their open sides were against 
the back of this tray. 

I am aware that the number of words necessary for describing this little 
piece of apparatus makes it appear somewhat complicated, but if one will take 
a piece of paper of suitable dimensions and follow the description given, he 
will find that the making of a model of one of these trays is a very simple 
matter. 



CHAPTER IV 

GENERAL RELATIONS TO ENVIRONMENTAL FACTORS 

Benecke, W. Allgemeine Physiologic der Ernjihrung der Schizomyceten 
und der Eumycetem (Stoffwechsel). Lafar's Hdb. d. tech. Mykologie 1 : 

303-427- 

I. SAPROPHYTISM AND PARASITISM 

Since the fungi are those classes of plants low in the series with 
respect to morphological complexity which possess no chlorophyll, 
they are unable to utilize the carbon dioxid of the air, and like in- 
sects and other animals they require their carbon in organic com- 
binations. They are accordingly associated with organic matter, 
living or dead. The plant pathologist devotes primary attention to 
those fungi inducing injuries sufficient to be termed plant diseases. 
Interest is, of course, attached also to any parasitic species ; that 
is, to any which may penetrate and develop within or upon the 
tissues of another plant, but the nature and extent of the disturb- 
ances which result offer the special problems and make necessary 
the special field of the pathologist. 

The habitats of the majority of the fungi are situations in which 
organic matter is available through the decay of dead things. In- 
deed the fungi take a prominent part in decay, or the return of 
organic matter to more elementary combinations. Forest and field, 
therefore, abound in species, whether evident or not to the popu- 
lar eye. The fungi associated with decaying materials only are 
termed saprophytes {nictatrophs). Theoretically, the pathologist is 
not concerned with this class of organisms. On the other hand, 
a very considerable part of the fungi obtain their organic nutrients 
by penetrating a living organism as host and growing in inti- 
mate association with its body. Such fungi are termed parasites 
{paratrophs). The parasitic fungi are, for the most part, parasitic 
upon plants, although small groups are confined very largely to 
insects, and a few species affect higher animals. 

62 



ENVIRONMENTAL FACTORS 63 

Considering the fungi as a whole, there is necessarily no sharp 
line of demarcation between the saprophytic and the parasitic habit. 
Some organisms which attain their best development as parasites 
may, if occasion demands it, sustain themselves saprophytically, 
or they may normally undergo a portion of their existence as sapro- 
phytes. The converse of this is also true. With respect to this 
habit four subdivisions may be recognized. 

Obligate parasites are, practically speaking, entirely dependent 
upon other living things for requisite Conditions of growth and 
particularly, perhaps, for the organic nutrients. 

Obligate saprophytes grow upon nonliving substances and are 
unable to penetrate living tissues. 

Facultative saprophytes are organisms which normally pass 
through life as parasites, but which are capable for a time, or in 
certain stages of development, of a true saprophytic existence. 

Facultative parasites are saprophytes which only occasionally, 
or under very special conditions, may become parasitic. 

In making these distinctions it should not be assumed that 
special weight is given to the form of the organic food materials 
utilized by the fungus, since it is quite probable that a parasite on 
the one hand and a saprophyte on the other may secure from its 
host or from the substratum precisely the same compounds. Bio- 
logical relations should be regarded as most important. For general 
descriptive purposes and for biological discussion the classification 
mentioned above is a matter of convenience, but opinions would vary 
greatly if it were necessary to apply this specifically. 

The group in which obligate parasitism seems most clearly de- 
fined is that of the rusts, Uredinales. It would be useless to try to 
cultivate these fungi in nonliving substrata, that is, in artificial 
cultures. The germination of the spores alone may proceed apart 
from the host. In such groups as the Chytridiales and the downy 
mildews, Peronosporaceas, the majority are obligate parasites ; yet 
a few of the former order, and species of Phytophthora in the 
latter family, have been grown on dead substrata. The smuts, 
Ustilaginales, and the plum pockets and witches' brooms of stone 
fruits, Exoascaceas, are strictly parasitic, although upon artificial 
media the conidia of many species may sprout vigorously. The sur- 
face mildews, Erysiphaceae, are doubtless also properly classed here. 



64 PHYSIOLOGICAL RELATIONS 

The obligate saprophytes include many of the mushrooms, 
Basidiomycetes, and common molds of diverse families. 

Most of the important disease-producing fungi popularly known 
as leaf spots, cankers, stem rots, etc., are capable of vigorous 
growth in artificial culture, and some even produce normal fruit 
bodies under such conditions. These fungi are commonly Asco- 
mycetes and Basidiomycetes. In nature many organisms belong- 
ing to these classes develop and mature their fruit bodies, especially 
the perfect stages, only after the infested parts are dead and 
fallen. 

The facultative parasites are found especially among the groups 
mentioned in the last paragraph and also among the black molds, 
Mucoraceae. Fungi which are ordinarily common upon decaying 
logs, or destructive to timber, may occasionally develop as para- 
sites on living trees. The black mold, Mncor imiccdo, so common 
in the household, may under certain conditions cause a serious rot 
of sweet potatoes, and it has been known to injure some plants in 
the seedling stage. The conditions under which such saprophytes 
become parasitic are not always clearly understood. In general it 
is evident that some condition of the environment has operated to 
render the host plant less resistant, or else the conditions have 
been such as to develop exceptional vigor in the fungus. Almost 
as long as fungous diseases have been known there has existed 
the belief that such diseases in any given host plant are in some 
way dependent upon a certain lack of vigor in the plant. Practical 
growers and many plant pathologists have held that vigorous, well- 
cultivated, and well-nourished plants mean plants resistant to disease. 
No one would question the general desirability of resistant plants, 
yet this attitude requires special comment and treatment. 

A very large number of the obligate parasites and some fungi 
less obligatorily parasitic are, or seem to be, specially endowed with 
the ability to enter relatively vigorous growing organs of the plant. 
The majority of the fungi, moreover, do not kill immediately the 
tissues which they invade. All sorts of deformities, including 
witches' brooms, may appear as a result of the association ; but so 
long as the fungus is rapidly growing, it seems generally to have 
a well-established relation with the living cells, such that when the 
invaded tissues die, the fungus spends itself in reproduction. 



ENVIRONMENTAL FACTORS 65 

In contrast to those just mentioned, there is that general sub- 
division of diseases which we have designated as leaf spots, stem 
rots, and fruit decays. The fungi producing these affections fre- 
quently, though by no means always, kill the tissues as they pene- 
trate the host. In other cases they enter and produce disease only 
when the affected parts have suffered some injury, overstimulation, 
or drying out. In the case of fruits they are proverbially destructive 
when the fruits approach maturity. In other words, a very large 
number of the fungi here included are not in very close associa- 
tion with living tissues, and are, from several points of view, 
hemiparasitic. It is to be emphasized, however, that many of our 
disastrous fungous diseases are included in this subdivision. Now 
in the case of the strictly parasitic fungi already referred to, it is 
very doubtful if vigor of the host is alone sufficient to prevent 
disease. In fact, some of the most vigorous varieties (whether 
judged by vegetative or fruiting achievements) have been particu- 
larly susceptible to certain diseases. Before adopting the view that 
all ills flee before vigor we must make ourselves clear as to what 
vigor means. If it is synonymous with resistance to disease, then 
of course all plants subject to disease under any conditions are 
nonvigorous. Many wild or native prototypes of certain highly 
responsive, cultivated varieties when grown side by side with the 
latter may show more, or may show less resistance to disease, 
wholly independent of robustness. It does not at all hold that 
factors which favor the fullest development of the host may not 
also encourage the fungus. Moreover, factors unfavorable to the 
host may be similarly unfavorable to the fungus. 

Phytophthora infestans, Plasmopara Viticola, and Cystopus can- 
didns, on some of their hosts, — the potato, the grape, and the 
shepherd's purse respectively, — would seem often to be most 
effective when the host is growing vigorously. Ward has suggested 
from experiments with the rust on brome grass that any hindrance 
to free nutrition of the host is likewise a means of inhibiting the 
fungus. 

In the case of fungi whose weapons for attack are most effect- 
ive where the plant is least alive, so to speak, — as when the 
leaves have been injured by drought or other causes, or when the 
fruit is maturing, — it is then clear that any environmental factor 



66 PHYSIOLOGICAL RELATIONS 

promoting a healthy growth of all parts of the host throughout the 
season would decrease disease. 

After all, saprophytism and parasitism are terms of degree, and 
organisms are classed as possessing the one habit or the other 
simply upon general evidence, or macroscopic appearances. It is 
quite possible, however, that in an ultimate analysis of the associa- 
tion of host and parasite, or of the method of fungous attack, 
many organisms now regarded as parasitic would be found to show 
a true saprophytic habit. It is possible that such organisms may 
gain entrance to the host through injuries ; in other words, estab- 
lish themselves in association with dead cells. By growth in these 
cells the excretion of acids and other diffusible products might 
bring about death in other cells in the vicinity, to which the fungus 
eventually spreads. So far as the actual presence of the fungus is 
concerned, therefore, there would be no direct association with a 
living cell in order to secure organic nutrients. This method of 
attack has been demonstrated to be that followed by Botrytis cincrea, 
a common greenhouse fungus. 

II. GENERAL RELATIONS TO CLIMATOLOGICAL FACTORS 

Experiment and observation alike demonstrate that the abun- 
dance of a very large number of fungous diseases is directly con- 
nected with or conditioned by climatological factors. With respect 
to conditions in the open, climatological factors are generally under- 
stood to mean water (moisture), light, temperature, and wind. 
These factors may affect independently host and parasite, and they 
may affect the interrelations of these organisms. Moreover, it is 
often difficult to interpret what factor is finally operative, or it is 
difficult to determine what are direct and what indirect effects of 
these environmental conditions upon host and fungus. In many 
instances it would be merely hypothetical with the data at hand — 
largely observational — to do more than designate cerUun apparent 
or proximate causes. 

Moisture. Many fungous diseases are directly associated with 
abundant precipitation, or a humid atmosphere. There is no more 
conspicuous example of this than the brown rot of stone fruits — 
a disease which, in moist weather, has repeatedly crippled the 
peach industry. The association of epidemics of such diseases as 



ENVIRONMENTAL FACTORS 67 

black rot of the grape, apple scab, and late blight of the potato 
with humidity is a matter of almost annual record. 

Moisture generally augments the production of spores, and it is, 
of course, essential to the germination of these. It may at times, 
however, have another effect, — that of promoting the suscepti- 
bility of the host to attack. The potato appears to be more readily 
affected by the Phytophthora when it has at least sufficient water 
for vigorous growth. Kiihn observed that there are two stages of 
growth when the plant is most susceptible, first, when the plant is 
young and tender, and second, when tuber formation begins more 
vigorously. Ward tliinks these two stages correspond to periods 
of rapid movement of water and soluble food materials. 

He has also cited certain conditions under which Botrytis cin- 
erca is parasitic, and the suffusion of the host with water is a 
prominent feature of this case. 

It is commonly stated by grape growers that not only is the 
black rot of this fruit most abundant in humid weather, but that,' 
further, it is more abundant upon vines which have made a vigor- 
ous '" sappy " growth. This would indicate that moisture acts here 
also indirectly to render the host more sensitive. 

Psciidouwnas cainpcstris, producing the black rot of cabbage, 
gains entrance to its host by reason of beads of water over the 
marginal water pores of the leaf. These droplets are, when there 
is sufficient soil moisture, a normal occurrence on cool mornings 
succeeding warm days. It signifies a state of "guttation," and, 
practically speaking, means a water way between the external and 
internal environment. 

Smith and Stone (see asparagus rust) have demonstrated an 
interesting water relation as affecting the prevalence of the rust of 
asparagus. The fact that chrysanthemum rust may be largely 
controlled by subirrigation, and carnation rust greatly reduced by 
the same treatment, is perhaps to be explained simply by the 
prevention of germination. 

An examination of the conditions under which epidemics occur 
in the case of such fungi as the leaf blight of celery, leaf spot of 
strawberry, and many others lead to some interesting suggestions. 
These diseases may disappear during a moist summer, which 
affords a relatively succulent growth of the hosts. In fact, such 



68 PHYSIOLOGICAL RELATIONS 

blights mentioned seem to profit materially from severe alterna- 
tions or contrasts of weather conditions. Moreover, if heavy dews 
prevail during a warm summer these fungi spread irrespective of 
precipitation. In such cases it is apparent that injured or drying 
portions of the plant are at least the first seats of disease. It seems 
to be true that many crop diseases are commonly most important 
under conditions of moisture insufficient for most vigorous crop 
production. 

Light. The chief role of light in plant economy is connected 
with the formation of sugar and starch, from which, in large part, 
the other organic products are ultimately derived. Light, how- 
ever, calls forth a variety of responses in every green plant, and 
it may play a direct or indirect role in the relation with parasitic 
fungi. It has long been observed that celery under lath or cloth 
screens, that is, half shade, is largely free from the early blight. 
The leaf spot or so-called rust on the strawberry may be similarly 
controlled through reduction of the light factor with the increased 
humidity and diminished evaporation generally incident thereupon. 
It is also reported that the tent cloth is effective against asparagus 
rust. Ginseng growers in New York and Missouri are employing 
the lath screen advantageously in the prevention of a serious blight 
of this plant, due to a fungus which is believed to gain entrance 
most readily at the margin of the leaf, possibly following a tend- 
ency to sun scald in that area.. Screening, however, is not advised 
for strawberries, and it would be available in the home garden, in 
general, only where such a device may be at will readily interposed 
or removed. In opposition to these beneficial effects of half shade, 
we have also abundant observations showing that certain powdery 
mildews are far more effective as parasites under just such con- 
ditions as above enumerated. I have seen wheat under partial 
shade badly infested with the powdery mildew, which in the 
central West, at least, is seldom, if ever, seen in the open. Time 
and again, in that same region, one may observe that in the case 
of well-watered lawns the mildew of blue grass abounds in a circle 
rather sharply limited by the heavier shadow areas of trees. Simi- 
larly, in the drier West the grape mildew is, as a rule, found mostly 
on Vitis vinifera stock, and in shaded places. The fungus soon 
disappears from leaves to which strong sunlight is admitted. 



ENVIRONMENTAL FACTORS 69 

Strawberry mildew is also far more abundant in shaded localities. 
It is a matter of common observation that while cucumbers fre- 
quently mildew under greenhouse conditions, yet in the open the 
cucumber mildew is very seldom observed upon this host, at least 
in the eastern and central United States. It is claimed that cer- 
tain greenhouse plants are more subject to the attack of the com- 
mon gray mold, Botiytis, when partially etiolated, and De Bary, it 
seems, was able to predispose Petunia to the attack of Botrytis 
through etiolation. 

It is apparent that in so far as screen mechanisms largely pre- 
vent the formation of dew, it is probably in large part through 
this change in the moisture relation that they are important. 
There may also result a number of direct effects of light, for 
in the case of strongly etiolated or yellowed and attenuated 
plants, bud and stem diseases seem frequently to be more com- 
mon. Very little experimental study has been bestowed upon 
these relations. 

III. SPECIAL RELATIONS TO ENVIRONMENTAL FACTORS 

Temperature. Very little work has been done which bears 
more particularly upon the relation of parasitic fungi to various 
conditions of environment than to fungi in general. The results 
of the work available, however, will be of assistance to the stu- 
dent and investigator in using his culture work to the greatest 
advantage. 

The optiinmn. The optimum temperature for growth of a 
particular fungus in culture may not be the optimum tempera- 
ture for spore germination or for spore formation. It is difficult 
for observers to agree precisely in giving what is termed the 
optimum temperature for any fungus, since one observer may 
emphasize the total growth (dry weight), another the abundance 
of spore production, etc. The optimum temperature as given 
for the growth of various species of bacteria usually refers to 
the temperature at which the extent of the colony is greatest. 
Wiesner has studied in detail the relation to temperature, of 
{ci) germination, (b) visible mycelium development, and (r) spore 
formation in the saprophytic fungus Penicillhnn ghmcuvi. In 
the absence of data equally as good for parasitic fungi, the 



JO 



PHYSIOLOGICAL RELATIONS 



observations on the above-mentioned organism are here presented 
in tabular form. 



Temperature, ° C. 


Time to Germination 
(Days) 


Time to Production 

of Visible Mycelium 

(Days) 


Time to Spore 

Formation 

(Days) 


i-S 


5.80 






2.0 


5-5° 






2.5 


3.00 


6.00 




3-0 


2.50 


4.00 


9.00 


3-5 


2.25 


3-So 


8.00 


4.0 


2.00 


3.00 


775 


5.0 


1.50 


2.90 


7.00 


7.0 


1.20 


3.00 


6.25 


II.O 


1. 00 


2.30 


4.00 


14.0 


075 


2.00 


3.00 


17.0 


075 


2.00 


3.00 


22.0 (opt.) 


0.25 


1. 00 


1.50 


26.0 


0.50 


0.99 


2.00 


32.0 


0.70 


l.OI 


2.10 


38.0 


0-55 


2.25 


2.60 


40.0 


0.70 


2.50 


3-50 



In the above case it happens that the optimum for germination 
corresponds very closely with that for the formation of a visible 
mycelium and for the beginning of spore production, but this will 
not hold for all fungi. In general, the optimum temperature for 
the bacteria and fungi with which the pathologist is concerned 
would lie between 25° and 32° C, and it is customary to run an 
incubator in which ordinary cultures are being kept for vigorous 
growth and development at from 26° to 28° C. 

High temperatures. The thermal death points for vegetative 
cells of the bacteria and fungi have been variously determined 
to range from 40° to 75° C. As a rule, few fungi will grow 
above 40°, and to this temperature most of these organisms will, 
after a time, succumb. Nevertheless, both fungi and bacteria are 
able in one stage or another to survive considerable extremes of 
heat and cold. The parasitic organisms in general are vegeta- 
tively vigorous within far narrower limits than those of sapro- 
phytic origin, which latter are, for the most part, in nature 
subjected to greater extremes of conditions during the growing 
period. 



ENVIRONMENTAL FACTORS 7 1 

It is well known that spores of bacteria, unlike the vegetative 
cells, are extremely resistant to heat, — an exposure of one or two 
hours at the boiling point often fails to kill the more resistant 
forms. Likewise, it has been supposed that spores of fungi are 
similarly more resistant than the vegetative condition. This has 
not been found to be true in the case of SporotricJuivi globu- 
lifcruvi} and it was demonstrated in my laboratory that spores 
(conidia) of five forms — Aspergillus nigcr, Aspergillus flavus, 
Penieilliuui sp., Botrytis vulgaris, and Rhi::opus nigricans — differ 
very slightly as to the thermal death point from that of the vege- 
tative hyphae.^ Nevertheless, some spores of even parasitic forms 
are particularly resistant. It would appear that sclerotial-like struc- 
tures of similar forms are also capable of withstanding high tem- 
peratures, but there is no data which can be presented. 

Loiv temperatures. In general, fungi are able to withstand very 
low temperatures. Few fungous spores are injured at 0° C. It 
will be found quite generally true that cultures of saprophytic or 
parasitic organisms may be frozen solid in freezing mixtures with- 
out unusual injury. The effects of winter conditions are not ordi- 
narily such as to destroy fungous spores to any great extent. 

Light. The ultimate effect of light of different intensities upon 
organisms may be manifest through injury, change of form, or 
special stimulation. The immediate cause of the particular in- 
fluence is always difficult to determine, as is true in cases of the 
action of most external agents. A considerable number of in- 
vestigators have studied the effects of light upon the living cells 
of fungi and bacteria with regard to its injurious action, inhibition, 
or stimulation of germination, and the effects upon growth and 
reproductive processes. In general those organisms seem most 
readily injured by light which are sensitive to many other exter- 
nal stimuli. Pathogenic bacteria and certain hyaline fungi with 
specially restricted life relations are soon killed by direct exposure 
to sunlight. Some saprophytic forms are more resistant, and dark- 
colored fungous spores or hyphae are far less influenced. Ward 
made fresh sowings of Bacillus anthracis in nutrient agar in 
Petri dishes, covering the dishes with glass or quartz plates, and 

1 Duggar, B. M. Bot. Gaz. 27 : 131-136. 1899. 

2 O'Brien, Abigail. Built. Torrey Bot. Club 29 : 170-172. 1900. 



72 



PHYSIOLOGICAL RELATIONS 



then pasting over the latter a black paper stencil. After an ex- 
posure to varying durations of sunlight or to the electric arc, 
the dishes were placed in the incubator. The resulting colonies 
developing show that an exposure of six hours to sunlight is 
sufficient to sterilize almost completely the agar in those areas of 
the dishes to which sunlight was admitted, corresponding to the 
stencil mark. He also threw a solar spectrum on cultures sim- 
ilarly made, and upon incubation it was demonstrated that the 
blue-violet rays are most injurious in their action. Since this kill- 
ing effect is not evident when the culture is exposed in a vac- 
uum, it would seem that the deleterious action is probably an 
oxidation effect. 

It may perhaps be inferred that light is more important in the 
destruction of the spores of parasitic fungi than are all other 
agencies combined. Nevertheless, many spores are well pro- 
tected against these deleterious effects. However this may be, 
a large number of fungous spores find hiding places under pro- 
tecting rifts of the bark, beneath the leaf scales, or in the debris 
on the surface of the soil, so that an adequate proportion survive 
the resting period, as a rule, to continue the prevalence of all 
common plant diseases. 

Many fungous forms are wholly independent of the presence 
of light as a requisite factor in normal development. On the 
other hand, in darkness the hymenophores of certain species 
are said to be abnormal in form. 

The results indicate that light has an injurious and retarding 
influence on the germination of fungous spores. De Bary records 
that certain members of the Peronosporacese, notably Phytoph- 
thora infestans, germinate with difficulty in daylight and not at 
all in sunlight, and Miss Ferguson and others have confirmed 
this observation in experiments with Agaricns campcstris and 
many other Hymenomycetes. Very little accurate information 
is at hand relative to the effects of light in the open upon the 
development of the fruiting stages of fungi. 

For all practical purposes in culture work with the fungi, the 
relation of light is not generally an important one. The studies 
which have been made, however, should be followed up from a 
quantitative point of view, for the exact effects of light intensities 



ENVIRONMENTAL FACTORS 73 

or quality upon form and color, metabolism, rate of growth, etc., 
are extremely important from a general physiological standpoint. 

Nutrients. The cultivation of fungi upon decoctions or in- 
fusions of organic substances, or upon solid organic substrata, 
would afford only through a tedious process of comparative study 
any fundamental ideas of fungous nutrition. The ease with which 
fungi may be grown in cultures and the use of synthesized culture 
media have afforded an opportunity for exact determination of the 
elements required by these organisms. There may be some specific 
variations, but it is now generally agreed that the majority of the 
fungi require nine elements, viz., carbon, hydrogen, oxygen, nitro- 
gen, sulfur, phosphorus, potassium, magnesium, and iron. 

Carbon. For most culturable fungi, whether primarily parasitic 
or saprophytic, carbon is available as grape or cane sugar, glycerin, 
asparagin, peptone, etc., in fact, in almost any soluble or readily 
convertible nontoxic form. It is to be inferred that the obligate 
parasite, as well, utilizes the soluble carbohydrates, peptones, etc., 
of the host cell, but its exact relations cannot well be determined. 
Owing to indirect needs in respiration, the nutrient solution must, 
in order to yield a considerable growth of the fungi, contain a 
relatively large proportion of carbohydrates. 

Nitrogen. Nitrogen may be furnished to the readily culturable 
fungi in the form of nitrates or ammonia compounds, but in some 
cases preferably as peptone, casein, or in other organic form. It is 
probable that the adaptations which result in obligate parasitism 
have only in part a special relation to the nitrogen food supply. 
Some fungi may be cultivated only with difficulty, and among these 
forms certain species are benefited by using as a substratum por- 
tions of the natural host (steamed), or decoctions prepared from 
the host plant. It is, however, possible that this relation is con- 
cerned with special stimuli, and has no bearing on the nitrogen 
factor. 

The relation of certain parasitic organisms to atmospheric nitro- 
gen has become unusually interesting. It has been shown by more 
than one observer that fixation of nitrogen by the various forms 
of the leguminous tubercle bacteria, Psendoniojias radicicola, may 
proceed in suitable artificial cultures. It proceeds, therefore, with- 
out reference to symbiotic association. 



74 



PHYSIOLOGICAL RFXATIONS 



Relatively striking results have been obtained by Saida ^ with the 
parasitic fungus, Phovia Bctce. Some data from cultures seventy- 
five days old with 50 cc. of media are as follows : 



Phoma BeT/E 



Substances added to a nutrient salt solution ^ 




Fixation of nitrogen, 
in milligrams 



Cane sugar 

Cane sugar 

Cane sugar (+ (NH4)2C03, trace) 
Cane sugar (4- (NH4)2C03, trace) 
Cane sugar (+ (NH4)2C03, trace) 
Cane sugar (+ (NH4)2C03, trace) 



■7393 
I. 1828 



1.7742 

3-5484 
6.2097 



More recently Ternetz ^ has isolated five endophytic mycorhizal 
fungi from certain Ericaceae, all of which have been found to be- 
long to the form genus Phoma. Three of these organisms, viz., 
Phoma radicis Vaccinii, Phoma radicis Oxy cocci, and Phoma 
radicis Andromeda, have shown a well-developed capacity for 
nitrogen fixation in culture, these three mentioned working even 
more economically than Azotobactcr cJiroococaim, the amount of 
nitrogen fixation in milligrams per gram of dextrose used, being, 
under the conditions of culture, respectively 22.14, 18.08, 10.92, 
and 10.66 for the four organisms mentioned."* 

The mineral nutrients may be supplied in the form of any of the 
soluble salts, the neutral salts being, in general, preferable. Formulae 
for culture solutions are, however, given under nutrient media. 

1 Saida, K. Ueber Assimilation freien Stickstoffes durch Schimmelpilze. Ber. 
d. deut. bot. Ges. 19 : (i07)-(ii5). 1901. 
^ This solution was constituted as follows : 

KH2PO4 0.4 

MgS04 0.4 

CaCl2 trace 

Water loo cc. 

3 Ternetz, Charlotte. Ueber die Assimilation des atmospharischen Stickstoffes 
durch Pilze. Jahr. f. wiss. Bot. 44 : 353-408. 1907. 

* Other papers of interest in connection with the fixation of nitrogen by fungi 
are the following : 
Puriewitsch, K. Ueber Stickstoffassimilation bei den Schimmelpilzen. Ber. d. 

deut. bot. Ges. 13 : 342-345. 1895. 
Froehlich, II. Stickstoffbindung durch einige auf abgestorbenen Pflanzen haufige 
Ilyphomyceten. Jahr f. wiss. Bot. 45 : 256-302. 1907. 



ENVIRONMENTAL FACTORS 



75 



Solutions. It has been the general experience that the readily 
culturable parasitic and hemiparasitic fungi have about the same 
relation to strengths of solu- n C 

tions as the saprophytic forms. 
Ordinarily, therefore, such 
forms give abundant growth 
under widely different condi- 
tions of concentration of the 
substratum. According to 
Eschenhagen the concentra- 
tions at which Botrytis ciiicrca 
may grow under ordinary cir- 
cumstances are as follows : 
grape sugar, 5 1 per cent ; 
cane sugar, 37 per cent ; 
sodium nitrate and calcium 
chloride, 16 per cent; sodium 
chloride, 12 per cent. In the 
culture work in the laboratory 
it will be found, however, that 

differences in the strength of Fig. 15. Cells of Ericaceae (after Ter- 
the culture medium will be netz), and Orchidace.^^ with Endophytic 

. 1 , ■ ,1 Mycorhiza, also Coralloii) Roots 

accompanied by noticeable 

differences in the form of the fungous colony, amount of the 
mycelium, and the character of the spores produced. 




CHAPTER V 

ARTIFICIAL INFECTION 

Infection experiments, or, as usually termed, artificial infection 
experiments, are essential in pathological work. They may be 
undertaken for a variety of purposes, among which the most 
important seem to be the following : 

1. To determine if a given organism is parasitic, or the cause 
of a particular disease. 

2. To determine the conditions under which an organism is 
most active in producing a disease, as well as the natural seat 
and manner of infection. 

3 . To determine the range of pathogenicity of a given organism ; 
that is, to demonstrate what varieties, species, genera, etc., may be 
considered, potentially at least, host plants. 

4. To determine the relationship .of the different stages of an 
organism to one another and to the host, or hosts. 

5 . To determine the conditions under which the different stages 
of a fungus may be developed. 

6. To determine the special relation of a parasitic organism to 
lesions or abnormalities of the host, with which a parasitic organism 
may be constantly associated. 

The rules of proof formulated by Koch, especially for disease- 
producing bacteria, have been repeatedly brought before investi- 
gators, yet they are too frequently ignored. They are appropriately 
termed the canons of Koch. They should be kept in mind in all 
pathological work, as they are applicable in all such studies, despite 
the exceptions which may sometimes be made. These rules may 
be expressed as follows : 

a. Under diverse conditions the fungus must be constantly and 
abundantly associated with the disease, or pathological state. 

b. The organism should be grown in pure cultures, when pos- 
sible, and its differential characteristics well studied. 

76 



ARTIFICIAL INFECTION 



11 



c. The characteristic disease should be produced by infection 
experiments with a pure culture. 

d. The fungus associated with the disease induced should be 
identified as the one originally separated, and any abnormalities of 
host should likewise correspond. 

The purposes of the infection experiments as above outlined 
are merely suggestive, and it is evident that a single series of 
experiments may give all or nearly all of the indications desired. 
Each subdivision, however, deserves special consideration. 

I. With such obligate parasites as the Peronosporacese, Exoas- 
caceae, Erysiphaceae, Ustilaginales, Uredinales, and some others, the 




Fig. i6. Correct Use of Bell Glasses in Certain Types of Infection 
Work. (Photograph by Geo. M. Reed) 

constant association of an organism with a diseased condition would 
usually be sufficient to denote this organism as the cause of the 
disease. The conditions required for spore germination are in many 
cases unknown, and therefore negative results would be of no great 
value. There is therefore a two-sided opportunity for study. It 
would, however, be absurd to say that Empusa Mtiscce is not the 
cause of the well-known, or commonly observed, fly disease. Yet, 
so far as the writer is aware, no work has been done which would 
be counted as successful in the artificial propagation of such dis- 
eases among insects. With most groups of fungi and with the 
bacteria, infection experiments must be made if the work in hand 



78 PHYSIOLOGICAL RELATIONS 

pretends to be authoritative. It is true that the great majority of 
fungi described as the causes of plant diseases have not undergone 
experimental tests, although it will be admitted by most experi- 
enced pathologists that a large proportion of the claims made are 
just, beyond all question. Where the spore-bearing parts of a 
fungus emerge directly from only slightly injured tissues, or in 
other equally plausible cases, the statement of parasitism made by 
an experienced pathologist is usually correct. In all cases where 
decay has set in, or where there is great discoloration of the parts 
affected, — especially in root and stem diseases, leaf spots, leaf 
burns, etc., — experiments are necessary to determine the primary 
cause of the disease. 

It is often the case that the fruit bodies or the mycelial stages 
of several different fungi are found associated with a diseased con- 
dition, and it is necessary to determine either which fungus is the 
real cause of the trouble, or what part each one may play in the 
effect produced. All organisms must be isolated, and separate in- 
fection experiments should be made with each. In such cases, of 
course, the fungi may be only secondary, appearing more as sapro- 
phytes on plants which are diseased owing to the action of some 
more general environmental factor, to the injuries of some insect, 
or to a mechanical agent. In many instances the fruit bodies of a 
causal fungus may not be formed until after the death of the plant, 
as is particularly true of the pyrenomycetous fungi. If not readily 
developed in culture, for comparison with those produced in nature, 
it will be necessary not only to make infection experiments with 
the pure cultures, but also with the spores produced in the open. 
In general, controlled infection experiments will be more rigor- 
ously demanded as our knowledge is advanced. There are propor- 
tionally few groups of fungi which may be designated saprophytic 
or parasitic in more than a relative sense. 

2. Infection experiments often enable one to determine the role 
which may be played in the predisposition to attack by such con- 
ditions as excessive moisture in the atmosphere or soil, the state 
of nutrition of the host, etc. Excessive moisture in the soil and 
the crowding together of seedlings offer advantageous conditions 
for the outbreak of damping-off diseases, produced by such fungi 
as Rhizoctonia and Pythium. Moisture on the leaf surfaces favors 



ARTIFICIAL INFECTION 



79 



the spread of many fungi under the more or less "forced " condi- 
tions of the greenhouses. Overhead watering or the general sprin- 
kling of plants is sometimes alone sufficient to facilitate greatly 
the spread of disease, as in the case of the rust of chrysanthemums. 
Unusual succulence in the pear is said to be a favorable condition 
for infection by the pear blight organism. In general, it is believed 
that any conditions leading to the suffusion of the tissues of the 
host with water invite disease, particularly disease accompanied by 
the general destruction of the tissues, and finally by decay. 

From extended observations Atkinson was able to say that the 
absence of a sufficient amount of potash in the soil predisposes the 
cotton plant to the attacks of Macj-osporium nigricantiinn, which 
fungus is then the cause of a new and graver phase of the disease. 
Many analogous cases might be cited, all of which suggest the 
necessity of experimental work from the standpoint of inoculation. 
Recently Ward has reported that the lack, or poverty, of one or 
more necessary elements in the nutrition of the brome grasses does 
not seem to predispose those hosts to the rust fungi parasitic upon 
them. It may well be inquired if this is a special case, and particu- 
larly if there may be any difference in this regard between obligate 
and facultative parasites. In this connection, moreover, the experi- 
ments made by Salmon with ErysipJic graniinis may be cited. He 
found that a wound sometimes sufficed to break down completely 
the immunity of certain species of grasses to a particular form, or 
race, of this fungus. 

The method of penetration of the germ tube of the fungus can 
only be definitely determined by careful infection experiments. It 
is just as true for a fungous disease of plants as for a bacterial dis- 
ease that a thorough study of the conditions has not been made 
until the possible methods of infection are determined. Not only 
is it necessaiy in the general etiology of the disease, but extremely 
important in the formulation of preventive measures. Fungi gain- 
ing entrance only through injuries or wounds are, in general, much 
more readily suppressed or confined. 

3. Inoculation studies with certain species of Gloeosporium have 
indicated that many distinctly disease-producing organisms may 
have a considerable range of host plants. A species of "Rhizoc- 
tonia " (Corticium vagitm B. & C, var. Sohmi Burt) causing a 



8o PHYSIOLOGICAL RELATIONS 

rot of sugar beets may cause damping-off diseases of seedlings, as 
well as other diseases, in several different families of hosts. Of 
the numerous cases which might be cited in this connection, many 
are in need of critical study, notably Exoascus. Among hemi- 
parasites, or facultative parasites, such studies will doubtless lead 
to a considerable reduction in the number of the so-called species 
of such fungi. On the other hand, infection experiments have 
compelled mycologists to break up among others the old species 
Puccinia graviinis into several forms, frequently termed biological 
or physiological forms, or subspecies, which, in some cases, are 
entirely indistinguishable one from another on purely morpho- 
logical grounds. Each form has a restricted number of host plants, 
and it is believed that no cross infections occur. Many similar 
cases have been clearly demonstrated for the Uredinales, 

It has recently been shown that certain mildews, notably Erysiphe 
graminis, may likewise be broken up into forms restricted each to 
one or more host plants. The two fungi mentioned are instances 
where each parasite, as a species, is capable of infecting a large 
number of host plants. It remains to be seen to what extent such 
differentiation of forms is to be found in species more restricted 
as to host plants. 

4, Experimental evidence was required to demonstrate the long- 
suspected connection between Piiccmia graminis, the grain rust, 
and the common secidium on the barberry, yEcidiuin Berberidis. 
Those experiments, although preceded by studies in heteroecism 
upon Gymnosporangium, mark a very distinct epoch in infection 
work, for heteroecism has proven a very important biological phe- 
nomenon. Within the past few years, particularly, much has been 
done towards a systematic endeavor to connect by experimental 
proof the heteroecious forms of Uredinales, Nevertheless, much 
valuable work remains to be done, and the observant student will 
constantly find suggestions in the proximity of host plants taken 
in connection with the sequence of stages in these fungi. It is 
well known that the occurrence of a uredo or teluto stage in con- 
nection with an ascidium, or closely following the latter, is not the 
final proof that these stages are connected. A close observation of 
many affected host plants during different seasons may, however, 
give some valuable clews as to relationships and prevent fruitless 



ARTIFICIAL INFECTION 8 1 

experimentation. Finally, in this it is again to be urged that in a 
study of the relationship of stages to one another and to the host 
plant, by artificial infection, experiments should be made upon 
properly isolated hosts. 

5. In some regions the production of the oospores of such fungi 
as Cyst op J IS candidns and Cyst op us Bliti are practically unknown ; 
yet in other regions, and during certain seasons, the oospores are 
produced in great abundance. A somewhat similar fact is the con- 
tinuous production of conidia by some species of Erysiphacese in 
certain habitats. Together with infection experiments under differ- 
ent conditions, and upon host plants of various ages, physiological 
studies of the host will be required. 

6. It is well known that certain Uredinales and Exoascaceae are 
the immediate causes of the witches' brooms of the hosts in con- 
nection with which these fungi are found. On the other hand, 
SphcBrotheca phytoptop/iila grows only upon branches deformed by 
phytoptids. Fungi are associated also with many abnormalities 
commonly referred to as knots, cankers, etc., and in nearly all such 
cases infection experiments should be called into service to deter- 
mine not merely if the fungus is parasitic, but also to determine 
if it is the primary cause of the abnormal development. Even if 
the fungus is known to be parasitic, from the point of view of 
pathology, the fungus becomes a matter of secondary importance 
when it is parasitic merely in consequence of some other injury or 
excitation. 

In general, infection experiments may be carried out either in 
the open or in the greenhouse. Frequently it is possible to study 
natural infections. Nevertheless, adequate opportunities for plant 
pathological work have not been secured until a good greenhouse 
is constantly available. 

The methods of making inoculations are necessarily various but 
always simple. With such fungi as the rusts, mildews, and many 
species producing leaf spots, the germ tubes usually gain entrance 
by boring through the epidermis or by passing in at the stomata. 
No injuries or abrasions of the organs inoculated being necessary, 
the plant may be moistened, preferably by vigorous spraying, with 
distilled water. Bell glasses may often be employed if ventilation 
is provided (Fig. 16). In some cases perfect precautions iii2(st be 



PHYSIOLOGICAL RELATIONS 




taken to prevent the access of any spores from other sources. 
Ordinarily, precaution is fairly well secured by a sufficient number 
of control plants. 

If the spores of a given fungus are obtainable in quantity, these 
may be sprayed on the plant with an atomizer or small pump. A 

small number of spores may be 
sponged on or applied with a 
camel 's-hair brush. If the inoc- 
ulations are made towards even- 
ing, and the plants are wrapped 
loosely with paper or cloth, a 
moist condition may be readily 
maintained for a period suffi- 
ciently long. The cylindrical, 
open-topped, glass, insect breed- 
ing-cage is extremely useful as a 
cover for inoculated herbaceous 
plants of small size (Fig. 17). 
The top may be closed with a 
cloth, and thus ventilation is 
well provided for, while the 
moisture retained is usually 
sufficient. It insures, also, pro- 
tection against insects, but not 
against wind-blown spores. Tall 
bell glasses may be used when an atmosphere practically saturated 
is not objectionable. In this case, moreover, a relatively favorable 
state of humidity and aeration may be maintained by raising the 
bell glass on blocks. To provide against accidental infection great 
caution must be observed, as stated below. In the local inoculation 
of a twig, glass tubing may be slipped over the inoculated branch ; 
the ends of the tube may then be plugged first with moist and 
afterwards dry cotton. Glass vessels so employed may usually be 
removed within a few days. 

Bacteria and certain leaf spot and stem inhabiting fungi may" 
require wounding of the surfaces to which they are applied. The 
wounds may be made either with sterile needles, scalpels, or scissors, 
and the depth of such wounds must be determined by experience 



*>«»♦• 





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Hf^::- 


^m^ /J 


u". 


■ "t. "^ 




-,, ^ 


">■•,:>? 


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■ i^ ■ .-^ 




"^ 


'.^ 


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S:c-j.~ 


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liG. 17. Insect Breeding-Cage in 
Inoculation Experiments 



ARTIFICIAL INFECTION 



83 



and specific needs. In particular work the surface thus injured 
should be washed, cleansed with a disinfecting solution, if the struc- 
ture will permit, and again washed with distilled water before the 
inoculation is made. In work of this character the spores or 
mycelium for inoculation should be taken from a pure culture ; 
indeed, pure cultures should always be used if the fungi are cul- 
turable, except where the only 
material available is hopelessly 
mixed, and the inoculation is 
only desired to eliminate some 
of the saprophytic forms. It is 
usually well to cover the wounds 
with grafting wax (Fig. 18), or 
some other similar adhesive con- 
taining no injurious substance. 
This will be possible in the case 
of stem diseases. In this case 
the control experiments should 
be wounded and covered with 
wax as well, so that the condi- 
tions may be quite the same. In 
some instances absorbent cotton 
may replace the wax. 

Whenever the air may too 
readily serve as a source of con- 
tamination, plants of large size may be fairly well protected from 
this source of danger by using practically air-tight glass frames, into 
which the air may enter only after filtration through cotton, and 
smaller plants may be accommodated under bell glasses with open 
tops loosely plugged with cotton. 

Certain disease organisms gain entrance through the roots, as 
in the case of Ncocosmospora vasinfecta. It will be evident in 
such cases that the soil should be inoculated. If possible, the plants 
to be inoculated should be grown in sterilized soil, but another con- 
sideration of importance frequently is to have the soil conditions 
imitate as closely as possible the conditions under which the disease 
was developed in the field ; thus the type of soil and the percentage 
of soil moisture are important. 




Fig. 18. The Use uf Grafting Wax 
IN Inoculation Experiments 



84 PHYSIOLOGICAL RELATIONS 

In all cases inoculation experiments should be made in quantity, 
and control experiments in similar number must be relied upon to 
eliminate any possibility of error. If a given disease is particu- 
larly abundant in the region, and accidental infection therefore 
more probable, the number of control cultures should be further 
increased, in addition to the special precautions mentioned. 

A failure to secure infection from a relatively small number of 
experiments may not indicate that the particular fungus plays no 
part in the production of the disease with which it has been asso- 
ciated. At any rate, experience in pathological work is necessary 
when one assumes to make a positive statement in this regard. In 
some cases infection may occur at a definite period only, or closely 
related species of fungi may differ markedly with respect to the 
conditions under which infection may take place. It has been 
found that the fungus causing fruit spot of apple is effective at 
about the time that the hairs covering the surface of the young 
apple are broken off. The loose smut of oats penetrates the host 
only when the latter is in the seedling stage, while the smut of 
wheat may infect the blossom. 



CHAPTER VI 

THE PRINCIPLES OF DISEASE CONTROL 

Bain, S. M. The Action of Copper on Leaves with Special Reference to the 

Injurious Effects of Fungicides on Peach Foliage. Tenn. Agl. Exp. Sta. 

Built. (Vol.) 15 : 21-108. ph. 1-8. 1902. 
Burt, E. A. Resistance of Plants to Parasitic Fungi. Trans. Mass. Hort. 

Soc. (1898): 145-161. 
Clark, J. F. On the Toxic Properties of Some Copper Compounds with 

Special Reference to Bordeaux Mixture. Botan. Gaz. 33 : 26-48. Jigs. 

i-y. 1902. 
Hedrick, U. p. Bordeaux Injury. N. Y. Agl. Exp. Sta. Built. 287: 1-189. 

1907. 
Jacksox, H. S. Development of Disease Resistant Varieties of Plants. Trans. 

Mass. Hort. Soc. (1908): 123-137. 
Lodeman, E. G. The Spraying of Plants. 399 pp. g 2 Jigs. 1896. 
MiLLARDET, A. De Faction des melanges de sulfate de cuivre et de chaux sur 

le mildion. Compt. Rend. 101 : 929-932. 1885. 
Scott, W. M. Self-Boiled Lime-Sulphur Mixture as a Promising Fungicide. 

Bureau Plant Industry, U. S. Dept. Agl. Circular 1 : 1-18. Jigs. /, 2. 
(Spray Calendars and Bulletins of the Agl. Exp. Sta.'s in the United States.) 
Swingle, W. T. Bordeaux Mixture. Div. Veg. Phys. and Path., U. S. Dept. 

Agl. Built. 9: 1-37. 1896. 

I. METHODS OF CONTROL 

A proper knowledge of the life histories of parasitic fungi, ex- 
perience in the use of spray mixtures, an adequate conception of 
crop requirements, and a comprehension of general plant physiol- 
ogy make possible in the great majority of cases a rational means 
of disease control. 

Eradication, prevention, or control of fungous diseases may be 
brought about more or less successfully by proper regard for such 
factors as varietal resistance, seed selection, crop rotation, seed 
treatment, application of fungicides to the growing crop, and gen- 
eral sanitation. It is frequently necessary to combine several methods 
of procedure in combating the attacks of a single organism, and 
in no case should practices of general sanitation be disregarded. 

Resistant varieties. Notable instances of the resistance of par- 
ticular varieties of important parasitic fungi have been brought to 

85 



86 PHYSIOLOGICAL RELATIONS 

the attention of growers and pathologists from early times. It is, 
in fact, seldom that all the individuals of even a well-established 
variety are equally susceptible to disease, and the differences be- 
tween closely related varieties are often surprisingly great. The 
Iron cowpea has been shown to be far more resistant than other 
varieties to the wilt disease, and a new strain of cotton, the Dillon, 
possesses similar qualities with respect to the same fungus. Every 
carnation grower became familiar a few years ago with the fact that 
the Scot carnation was peculiarly susceptible to carnation rust, and 
that under ordinary conditions the Enchantress was peculiarly re- 
sistant. The Kieffer pear is far less attacked by blight and leaf 
spot fungi than other varieties commonly grown. Nearly all fruits, 
vegetables, field crops, and floricultural plants will, upon careful 
investigation, give evidence of more or less striking qualities of re- 
sistance. This resistance may be inherited, or it may be a charac- 
teristic which changes markedly as the climatic or soil conditions 
vary under which the host plant may be growing. The relations 
to disease may, therefore, be complex, and it is not the purpose of 
this summary account of disease control to describe at length the 
diverse relations of host and parasite. 

Seed selection. Seed selection is, in many cases, the easiest 
and most natural method of disease control. The anthracnose of 
beans is carried over from crop to crop very largely by means of 
diseased seed, and it has been shown that diseased pods mean as 
a rule diseased seed, that treatment of such diseased seed is not 
effective, and that, therefore, the most rational method of combat- 
ing the organism is to plant seed from selected pods. It is very 
probable that the anthracnose of cotton is similarly transferred 
from year to year. Certainly the appearance of the anthracnose 
abundantly upon the seedlings, especially upon the cotton leaves, 
suggests the presence of the organism in the seed. The late blight 
of potato seems to be commonly, if not entirely, tarried over from 
season to season by means of diseased tubers, the latter being in- 
fected with a form of the disease known as the potato rot. The 
selection of seed from a field in which no blight has been present 
to a very large extent insures a crop free from blight. Seed selec- 
tion is already practiced to a considerable extent, but there is no 
line of disease control requiring more attention at the present time. 



thb: principles of disease control 87 

Crop rotation. There is no small number of fungous diseases 
which reappear year after year on account of the fact that the soil 
has become contaminated with the spores or mycelium of the fun- 
gus, these stages being often able to remain alive throughout a 
considerable period of time. It is only possible to prevent many 
of these diseases by the practice of a suitable rotation. Land 
infested with the organism causing club root of cabbage and tur- 
nips should be kept free from cruciferous plants for two years. 
The fungus producing scab of potatoes is far more persistent in 
the soil than the last mentioned ; and Urocystis Cepulcc, the onion- 
smut organism, is supposedly able to retain the capacity for ger- 
mination in the soil for a number of years. In addition, there are 
many other fungous, as well as bacterial, diseases for which it is 
essential to practice the strictest rotation principles. 

The application of fungicides. The application of fungicides to 
the growing crop has been for about twenty years a principal means 
of disease control or prevention. In this connection it is under- 
stood that the application of a fungicide to the host plant is gener- 
ally for the purpose of protecting it from an attack of a fungus. 
In only a few cases is it possible to actually kill an organism which 
is already causing injury. In the case of some of the powdery mil- 
dews the use of any fungicidal sprays or dusts may be beneficial, 
in part, from the direct killing action of the fungicide upon the 
superficial growth of the fungus. In the great majority of instances 
the fungicide is applied with the view of covering a healthy plant, 
which is thus to be kept in healthy condition. The germination of 
the fungous spore, which may follow upon the host subsequent to the 
application of the fungicide, should thus be prevented. It has been 
fairly well demonstrated that the germinating spore will, for in- 
stance, absorb from the nearly insoluble copper compounds of 
Bordeaux mixture sufficient toxic substances to cause its death. 

At the same time, it is, of course, necessary that the fungicides 
shall be of a nature and strength which will be in general nonin- 
jurious to the plant which is to be protected. It is not, however, 
possible to determine this point precisely, since apparently under 
different climatic conditions the injurious action of the fungicide 
may vary greatly. Weak Bordeaux mixture will be noninjurious to 
the foliage of peach and plum, or even to apple, one season and 



S8 PHYSIOLOGICAL RELATIONS 

the following year applied with equal care the same mixture will 
cause great injury or defoliation. Moreover, since the various para- 
sitic fungi are differently affected by the strength as well as the 
composition of the fungicide, it is important to know the specific 
relations of each important parasitic organism. In the use of fun- 
gicides there is a very large field of investigation possible because 
of the fact that an intimate knowledge of the life histories of the 
organisms concerned alone affords a proper index of the best time 
for the application of the mixture, climatic conditions, and innu- 
merable other factors, serving also to modify the requirements in 
special cases. It has been possible to control very satisfactorily the 
blight fungi of potato, most of the commoner grape parasites, the 
bitter rot and scab of the apple, as well as numerous other diseases 
by proper use of Bordeaux mixture. Nevertheless, Bordeaux mix- 
ture should not be relied upon to the exclusion of other fungicides, 
nor is the indiscriminate use of any fungicide to be generally 
recommended. 

II. PREPARATION OF FUNGICIDES 

The more commonly employed of the many fungicides, which 
have been used by practical growers and plant pathologists, are 
as follows : Bordeaux mixture, ammoniacal copper carbonate, lime- 
sulfur wash, potassium sulfide, flowers of sulfur, copper sulfate, 
corrosive sublimate, and formalin. Of these preparations the 
first five may be employed upon the foliage during the growing 
condition of the plants. The remaining substances are generally 
used for disinfection of seeds and plants in dormant or winter 
condition. 

Bordeaux mixture. Bordeaux mixture is the most important 
and the most commonly employed of fungicides. As a rule it 
is true that Bordeaux mixture will protect a plant from fungous 
attack where it is possible to protect it by means of any spray 
mixture. Its injurious effects upon some plants preclude its 
use. In other cases the discoloration of fruits immediately before 
marketing would render them less desirable for market purposes, 
and again the discoloration of the foliage makes it objectionable 
in the case of ornamental plants. Bordeaux mixture may be used 
also for plants in dormant condition. Under such circumstances 



THE PRINCIPLES OF DISEASE CONTROL 89 

very strong solutions may be employed. The strength of solu- 
tion now generally regarded as a standard consists of : 

Copper sulfate . 5 lb. 

Stone lime 5 lb. 

Water 50 gal. 

A mixture of this strength is known as the 5-5-50 formula. 
The strength may be decreased or increased as desired, and it will 
be expressed in a similar manner, thus 2-2-50 and 10-10-50 
respectively refer to 2 pounds of each chemical and to 10 pounds 
of each in 50 gallons of water. The method of making Bordeaux 
consists in dissolving the required amount of copper sulfate in 
an equal number of gallons of water, the copper sulfate being 
placed in a sack and suspended in a barrel or other vessel, this 
method greatly facilitating the solution. 

The amount of lime required may be slowly slaked in another 
barrel or vessel and then brought up to a thick milk with a known 
quantity of water. This solution may be used as a stock solution, 
I gallon of the copper sulfate representing i pound of the copper 
salt, and i gallon of the lime milk representing i pound or more 
according as the mixture has been prepared. The amount of the 
copper solution for a barrel or tank may then be diluted practically 
to the capacity of the vessel employed, and then the fairly diluted 
lime milk is poured in, stirring constantly. It is desirable that the 
latter should be strained. The strong stock solutions should not 
be poured together. 

Ammoniacal copper carbonate. This preparation is frequently 
employed where a strong fungicide is needed, and where the 
color of the Bordeaux mixture renders it objectionable, the am- 
moniacal solution discoloring foliage to only a very slight extent. 
The constituents of this mixture are as follows : 

Copper carbonate 5 oz. 

Ammonia (26° Baume) 3 pt- 

Water 50 gal. 

The strong ammonia, which one must handle carefully, may be 
diluted to about five times its volume, and the copper carbonate 
may be rubbed up with water in a small vessel to form a thin 
paste. This paste is added to the now dilute ammonia with 



90 PHYSIOLOGICAL RELATIONS 

constant stirring. The mixture is then brought up to 50 gallons. 
Ammoniacal copper carbonate should be used as promptly as 
possible, owing to the rapid evaporation of the ammonia. 

Lime-sulfur wash. The lime-sulfur preparation which may be 
employed with least fear of injury to growing plants is a form 
known as "' self-cooked." It has been introduced relatively re- 
cently, and, therefore, has not been extensively employed by com- 
mercial growers. The constituents are as follows : 

Flowers of sulfur 10 lb. 

Stone lime 10 lb. 

Water 50 gal. 

The preparation of the mixture is simple. After weighing the 
lime into a barrel add three gallons of water, sift in the sulfur, 
and slake the lime slowly. As heating proceeds add more water 
and stir occasionally. The heat developed is sufficient to " cook " 
to the extent desired. When completely slaked cool promptly by 
diluting to fifty gallons. Patent preparations are made. 

Potassium sulfide. Potassium sulfide is a fungicide which is 
also employed when it is undesirable to have foliage discolored. 
It is, moreover, believed to be especially effective in the preven- 
tion of certain mildews, especially that of the goosebeny, and 
also the rust of carnations. This substance is sometimes known 
as liver of sulfur, and should, when fresh, make a solution 
yellowish brown. It is employed in the following preparation : 

Potassium sulfide 3-5 oz. 

Water 10 gal. 

Sulfur. P'lowers of sulfur is often surprisingly effective in the 
treatment of certain surface mildews, such as that of the rose. 
It may be dusted over the plants so as to fairly cover them with 
the yellow powder, and is particularly effective when the plants 
are wet. A paste of sulfur and lime is also employed by many 
growers in rose houses, the method of application being then to 
smear the steam pipes with the mixture, the fumes from which 
are disastrous to the mildew. 

Recently a sulfuric acid solution of a strength of i-iooo has 
also been successfully employed in the treatment of rose mildew 
and similar fungi. 



THE PRINCIPLES OF DISEASE CONTROL 91 

Copper sulfate. Copper sulfate is frequently employed as a 
wash for dormant trees and also for disinfecting seed of grains 
'which may be contaminated by adherent fungous spores. The 
solution may be prepared as suggested under Bordeaux mixture. 
When diluted, it should consist of : 

Copper sulfate i lb. 

Water 15 gal. 

It is seldom that one would desire to apply copper sulfate 
to the growing tree, on account of its injurious action upon the 
leaves, but occasionally it has been employed at a strength of 
I pound to 100 gallons of water. 

Corrosive sublimate. Bichloride of mercury, commonly known 
as corrosive sublimate, is an unusually strong poison for man as 
well as for animals ; at the same time it is a very effective disin- 
fectant and is very generally employed for potato scab. The 
solution consists of : 

Corrosive sublimate 2 oz. 

Water 15 gal. 

This is practically a solution of i-iooo by weight, a strength com- 
monly employed by physicians for disinfecting purposes. Seed 
potatoes which may have come in contact with the scab fungus 
should be soaked for one and a half hours in a solution of the 
strength indicated. This solution may also be used as an anti- 
septic dressing for wounds, especially after pruning. It should be 
made in a wooden or earthenware vessel, since it attacks metallic 
substances vigorously. 

Formalin. Formaldehyde vapor dissolved in water to give a 
solution which is ordinarily 40 per cent bears generally the com- 
mercial name formalin. It is like the last-mentioned fungicide, 
also a strong disinfectant, and is used very extensively for treating 
seed potatoes and seed oats and wheat. It should be employed of 
the following strength : 

Formalin i oz. 

Water 2 gal. 

Since formalin is a chemical which may be handled more con- 
veniently and with less danger than corrosive sublimate, it must be 
given the preference. 



92 PHYSIOLOGICAL RELATIONS 

Precautionary measures. Among the fungicides discussed arsen- 
ical poisons have not been included for the reason that they are 
supposed to be of importance only in the control of insect pests. 
Frequently it becomes desirable to combine an arsenical compound 
— Paris green, for instance — with Bordeaux mixture, and thus 
accomplish a double purpose. In that case more than a pound of 
lime, additional, should be included in the Bordeaux for each 
pound of the Paris green employed, otherwise injury may result. 

The lime-sulfur mixtures are now receiving attention through- 
out the country, and there are indications that they may become 
important. Experiments thus far show that the ordinary lime-sul- 
fur wash is much more toxic to sensitive foliage than the " self 
cooked." Growers should therefore clearly distinguish between 
these preparations. Moreover, the ordinary lime-sulfur is a kind 
of whitewash, and if employed when the fruit is approaching 
maturity, it may be objectionable in marketing. 



PART III 

FUNGOUS DISEASES OF PLANTS 

CHAPTER VII 

GENERAL CLASSIFICATION 

I. FUNGOUS DISEASES AND PATHOLOGY 

Comes, D. O. Crittogamia agraria. 600 pp. ly ph. 1891. 

Frank, A. B. Die Krankheiten der Pflanzen (Pilzparasitaren Krankheiten) 

2: 574 pp. 95 Jigs. 1896. Breslau. 
Freeman, E. M. Minnesota Plant Diseases (Report of the Survey, Bot. Series 

V). 432 pp. 211 figs. 1905. St. Paul. 
Hartig, R. Lehrbuch der Baumkrankheiten. 3d ed. 324 pp. 250 figs. 

1900. Berlin. (2d ed. transl. into English by Somerville and Marshall 

Ward. 331 pp. 159 figs. 1894.) 
KiJHN, J. Krankheiten der Kulturgewachse. 312 pp. 7 pis. 1858. Berlin. 
Masses, G. Text-book of Plant Diseases. 458 pp. 92 figs. 1896. 
Prillieux, Ed. Maladies des plantes agricoles et des arbres fruitiers et fores- 
tiers causdes par des parasites vegetaux 1 : 421 pp. 190 figs.; 2 : 592 pp. 

figs. 191-484. 
Smith, W. G. Diseases of Field and Garden Crops. 353 pp. 143 figs. 1884. 
Sorauer, p. Pflanzenkrankheiten 2 : (2d ed.) 456 pp. 18 pis. 21 figs. 1889. 

Berlin. (3d ed. revised by Lindau. 562 pp. 62 figs. 1908.) 
TuBEUF, K. vox, and Smith, W. G. Diseases of Plants induced by Crypto- 

gamic Parasites. 598 pp. 330 figs. 1897. 
UxGER, F. Die Exanthema der Pflanzen und einige mit diesen verwandte 

Krankheiten der Gewachse. 422 pp. 7 pis. 1833. 
Ward, H. Marshall. Timber and Some of its Diseases. 295 pp. 45 figs. 

1889. 
Ward, H. Marshall. Diseases in Plants. 309 pp. 1901. 

If we interpret disease as any apparently abnormal condition of 
an organism or of its parts or functions, it is evident that the 
diseases of plants, like those of other living things, include mor- 
phological and physiological disturbances which may be induced 
by a variety of environmental factors, living or nonliving. The 
popular conception excludes from the category of plant diseases 
those effects caused by predatory animals or by sudden mechanical 

93 



94 



FUNGOUS DISEASES OF PLANTS 



means. There is also a tendency to dissociate from plant diseases 
proper the widespread devastation which is the result of the varied 
injuries annually inflicted by insects. In general, therefore, we 
may disregard insects as the cause of plant diseases when that 
term is applied narrowly. 

It is within comparatively recent times that the specific injuries 
or modifications of climatic or other physical factors of the envi- 
ronment have been carefully studied. When properly understood, 
these effects have moreover frequently been termed " physiolo- 
gical " as opposed to "pathological." With a broad definition of 
pathological this interpretation would be illogical. Nevertheless 
the student of fungous diseases of plants has been the chief plant 
pathologist. This is partially due to the fact that the disease-pro- 
ducing fungi are intimately associated with the structure of plants, 
and a proper study of the fungus has necessitated a thorough com- 
prehension of its relation to the plant upon which it grows, the 
host. Plant diseases and plant pathology are, therefore, more or 
less synonymous with fungous diseases of plants, and the narrow 
use of the term plant pathology will on this account doubtless 
long persist. 

II. THE CLASSES OF FUNGI 

CoRDA, A. C. I. Icones Fungorum. (In 6 parts, large 4to.) 366 pp. 64 pis. 

1837-1857. 
Ellis, J. B., and Everhart, B. M. North American Pyrenomycetes. 793 pp. 

J I ph. 1892. 
Engler and Prantl (Eds.). Die natiirlichen Pflanzenfamilien 1 (1*): 57° PP- 

2(>3 fig^- / 1(1**): 5 1 3 PP- 2g3 figs. 
Farlow, W. G., and Seymour, A. B. A Provisional Host Index of the Fungi 

of the United States. 219 pp. 1 888-1 891. 
Saccardo, p. Sylloge Fungorum. (18 vols, to date.) 1 882-1906. 
Schroeter, J. Die Pilze (Cohn's Kryptogamen Flora von Schlesien), Pt. 1: 

814 pp.; Pt- 2 : 500 pp. i86g. 
Winter, G. Die Pilze (Rabenhorst's Kryptogamen Flora), Vol.1 (Pt. i): 

924 pp. 111.; Vol. 1 (Pt. 2): 928 pp. ill. 

Brefeld, O. Untersuchungen aus dem Gesammtgebiete der Mykologie. 

(Extensive; in 13 parts; illustrated.) 1872-1905. 
Cooke, M. C. Introduction to the Study of the Fungi. 360 pp. i4Sfigs. 1895. 
De Bary, a. (Transl. into English by Garnsey and Balfour.) Comparative 

Morphology and Biology of the Fungi, Mycetozoa, and Bacteria. 525 pp. 

198 figs. 1887. 
Lafar, Fr. (Ed.). Handbuch der technischen Mykologie. (In 5 vols.; 4 vols. 

complete to date.) 1: 749 pp. 2 pis. gjfigs.; 2: 503 pp. 10 pis. go 

figs.; 3: 573 PP- 37fig^-J 4: 558 pp. 122 figs. 1904- 



GENERAL CLASSIFICATION 95 

Tavel, F. VON. Vergleichende Morphologic der Pilze. 208 pp. go Jigs. 1892. 
TuLASNE, L. R. et C. Selecta Fungorum Carpologia. (In 3 vols.) 782 pp. 

64 pis. 1 861 -1 865. 
UxDERWOOU, L. M. Molds, Mildews, and Mushrooms. 214 pp. Q pis. 1899. 
ZoPF, W. Die Pilze. 500 pp. i6j figs. 1898. 

Every great division, or class, of the fungi contains some spe- 
cies capable of producing disease in other plants. Disease, in this 
connection, refers to a physiological disturbance, often accom- 
panied by anatomical injuries or hypertrophies. The number of 
such disease-producing organisms is sometimes very limited in a 
class, and there are orders in which no such organisms have been 
described. 

In a restricted sense the fungi may include only certain classes 
of chlorophyll-free thallophytes, but in the broader application of 
the term, it includes all chlorophyll-free organisms which may be 
regarded as plants. It is with this latter meaning that the term is 
here used, in so far as the general selection and arrangement of 
material is concerned, although this will not be permitted to affect 
the use of the word in a restricted sense as well. The fungi in- 
clude five well-marked classes of organisms, as follows : 

1. Myxoviycctcs. The slime molds. 

2. ScJiizoniycetcs. The bacteria. 

3. PJiycomycetcs. Water molds, black molds, downy mildews, 
etc., — algal-like fungi, 

4. Ascomycctes. The ascus-bearing fungi. 

5. Basidiomycctcs. Basidia-bearing fungi, — smuts, rusts, mush- 
rooms, etc. 

This grouping, however, shall not be taken to indicate a line of 
development beginning with the slime molds and advancing through 
the other groups to the smut and mushroom class. In fact, only 
the Phycomycetes, Ascomycetes, and Basidiomycetes, which have 
much in common, may be regarded as the true fungi, and nearly 
all the species here included have a filamentous vegetative stage. 
The bacteria form a coherent, distinct class, yet certain families 
show very close relationship with the fungi, while others show more 
striking resemblances to certain families of algae. The bacteria 
have, moreover, in no sense any very close animal-like allies. The 
Myxomycetes have no very apparent relationship with any other 



96 FUNGOUS DISEASES OF PLANTS 

groups of fungi or algae ; although in the lowest Phy corny cetes, 
perhaps, one may find a certain questionable similarity. However, 
it would seem that the closest allies of the Myxomycetes, as possi- 
bly of some of the lowest Phycomycetes, may be with the Plagel- 
lates. Finally the Myxomycetes resemble also in some characters 
other animal-like groups, such as the Sporozoa and the Myxospo- 
ridia. It is, however, unnecessary here to enter into a special dis- 
cussion of the relationship or homologies of any of these organisms. 



CHAPTER VIII 

MYXOMYCETES. SLIME MOLDS 

I. PHYTOMYXALES (PHYTOMYXACE^) 

In the family Phytomyxaceae are grouped the few disease- 
producing organisms among the Myxomycetes. The family is 
characterized by the production of naked masses of protoplasm 
(Plasmodia) within the cells of the host. The plasmodium gives rise 
simultaneously, or by a successive differentiation, to sphaeroidal 
spores, and the germination of the spore produces a motile swarm 
cell, by means of which distribution of the organism is effected. 
Generic differences are found almost wholly in the relation of the 
spores one to another, whether single or grouped. PlasmodiopJiora 
BrassiccB is the only well-known species of economic importance. 

II. CLUB ROOT OF CABBAGE AND OTHER CRUCIFERS 
Flasmodiopho7-a Brassicce Wor. 

Eycleshymer, A. C. Club-root in the United States. Journ. Myc. 7 : 79-87. 

pis. 13-16. 1892. 
Halsted, B. D. Club-root of Cabbage and its Allies. N. J. Agl. Exp. Sta. 

Built. 98: i-id. figs. i-ij. 1893. 
Nawaschin, S. Beobachtungen iiber den feineren Bau. u. Umwandlungen 

von Plasmodiophora. Flora 86 : 404-427. pi. 20. 1899. 
WoRONiN, M. Plasmodiophora Brassicae. Jahrb. f. wiss. Bot. 11 : 548-574. 

pis. ig-24. 1878. 

The club root, or club foot, is an unsightly and destructive root 
disease of crucifers which has been known in Europe for con- 
siderably more than a century. In England it is commonly called 
fingers and toes, anbury, etc. (Germany, Kohlhernie ; France, 
maladie digitoire). Our knowledge of the causal relations of a 
Myxomycete, Plasmodiophora, to the disease is primarily based 
upon the excellent researches of Woronin published in 1878. 

Habitat relations. In Europe the fungus is quite generally 
distributed throughout the market-gardening sections. In 1876 

97 



98 



FUNGOUS DISEASES OF PLANTS 



Woronin estimated the losses due to it in the vicinity of St. Peters- 
burg at $225,000. In the United States it has been disastrous in 
many of the northeastern states, particularly in those trucking 
regions which supply the markets of New York and Boston. 

It is, however, occasionally 
found both South and West. 
The limits of its distribution 
have not been clearly defined. 
Unquestionably it thrives best 
in a rich, warm, moisture- 
retaining soil. 

Seedling plants affected by 
this parasite show a decided 
flagging. ' ' They are stunted, 
unhealthy in appearance, and 
they may gradually die. P'ew 
of those affected when young 
reach maturity. The parasite 
attacks the roots and gains 
entrance to the parenchym- 
atous tissues. The presence of 
the organism within the cells 
affords a stimulus to abnormal 
growth. There results, in 
fact, malformities of striking 
appearance. These vary, on 
the one hand, from slight 
nodose swellings in the small 
rootlets, and knotty masses in 
the tough roots of some weeds, 
to the more or less irregular, 
but generally fusiform, digitate swellings (Pig. 19) in the cabbage, 
and the lobulated enlargements of the turnip. 

Many members of the mustard family, Cruciferae, are subject 
to the attacks of this fungus. A complete list of the hosts upon 
which it has been found cannot be given on account of the fact 
that much information has been covered up by too general state- 
ments. In the United States, however, it certainly occurs upon 




Fig. 19. Club Root of Cabbage, pro- 
duced BY PLASMODlOPHORABKASSICye'^OK 



MYXOMYCETES. SLIME MOLDS 



99 



varieties of cabbage, cauliflower and l^russels sprouts {Ih-assica 
olcracca), turnip {Brassica campcstris), rutabaga {Brassica Rapa), 
radishes {Rap/ia^ms sativa), and certain mustards (Sinapis and 
Brassica). It has also been found upon such weeds as shepherd's 
purse {Capsclla Bursa-pastoris) and hedge mustard {Sisyvibrumi 
officinale). In Europe besides most of the plants mentioned ]\Iathi- 




FiG. 20. A Cross Section of Cabbage Root affected by the Club 
Root Fungus. (Invaded cells enlarged and phloem tissue multiplied) 

ola incaiia and Ibcris unibcllata are hosts. There seems to be little 
recent data of interest bearing upon the comparative susceptibility 
of different varieties of cultivated plants. Many mistakes have 
doubdess been made in assigning to this fungus injuries appear- 
ing upon other orders of host plants, and sometimes even those 
upon crucifers, due to nematode worms. It is often difficult to 
distinguish between the two causes of disease. 



lOO 



FUNGOUS DISEASES OF PLANTS 



Morphology. Fungus and deformity. The parasite is sup- 
posed to gain entrance to the host plant during the swarmspore 
stage, or immediately upon leaving the swarmspore stage, there- 
fore in the amoeboidal form. No observations, however, have been 

made relative to 

m^yL^-^^jr-f. c 








Fig. 



host penetration, 
and the subject 
would doubtless 
prove an interest- 
ing one. 

A microscopic 
study of sections 
of the diseased 
root shows that 
the organism is 
most abundant in 
parenchymatous 
cells, often in the 
vicinity of the 
cambium. There 
21. Stages in the Differentiation of the is in quantity an 
Plasmodium and Spores in Plasmodiophora Brassic^ abnormal develoD- 
( After Nawaschin) 

ment of phloem. 
The xylem portions of affected roots are relatively inconspicuous. 
According to some observers, certain bundle elements may also 
show the parasite. 

The infested cells are ordinarily in groups (Fig. 20) and 
Nawaschin believes that these groups originate by the division 
of a single cell and that such groups may also transmit an in- 
fluence to similar tissues even at a distance, so that there may 
eventually result, for instance, histological disturbances in neigh- 
boring bundles. It is possible, however, that the young cells of 
the bundles may become infected and that the organism may be 
enabled to maintain itself in such cells for a time after differentia- 
tion of the latter as distinctive bundle elements. 

In an earlier stage the contents of the infected cells is of a half- 
fluid consistency, later turbid, and finally granular. Even in the 
first stage the parasite is noticeable in the amoeboidal form and 



MYXOMYCETES. SLIME MOLDS loi 

the nuclei may be distinct (Fig. 21, a). The number of amoebae is 
increased by division, probably by a kind of budding process. Starch 
is present in the host cells but the amoeba gives only a reaction for 
oil. No migration of the amoeboidal stage from cell to cell has 
been observed. Several nuclei are present in each amoeba, and as 
the number of the latter is increased they become rounded and 
pressed closely together into what is practically a plasmodium. 
The spore-forming stage is then initiated, accompanied first by 
peculiarities in the nuclei, which seem to disappear more or less, 
according to Nawaschin ; and this stage is followed, upon again 
clearly distinguishing the nuclei, by a new form of nuclear divi- 
sion, mitotic and simultaneous in all nuclei (Fig. 21, /; and c). 
There may be successive simultaneous divisions, and then the spores 
are differentiated by the formation of a cell wall around each nucleus 
and surrounding cytoplasm. Two stages in the differentiation of 
the spores are shown in Fig. 21, (^and c 

Olive ^ and Jahn ^ have recently described what seems to be a" 
sexual process in certain Myxomycetes (notably in Ceratiomyxa). 
It remains to be seen how these observations will finally be inter- 
preted, and further, if there may also be fusion of the nuclei in 
the case of Plasmodiophora. In this connection it may be stated, 
however, that some mycologists doubt the relationship of Plasmo- 
diophora with the Myxomycetes. 

At maturity most of the pathological cells are packed full of 
the spherical thick-walled spores, and the latter are perhaps set 
free only by the disintegration of the roots. Certain unusual 
appearances, moreover, have been described, but these are not 
understood. In from four to twenty-four hours the spores will 
germinate in water in which some of the host tissue has been 
teased out, the contents of each spore escaping in the form of an 
irregular protoplasmic mass which may quickly change its form. 
There is at first, for the most part, an appearance of an elongated 
process or cilium, which doubtless permits rapid motility, denoting 
also a swarmspore stage. In the swarmspore stage a nucleus and 

1 Olive, E. W. Cytological Studies on Ceratiomyxa. Trans. Wis. Acad. Sci., 
Arts and Letters 15 (2) : 753-774. 1907. 

2 Jahn, E. Myxomycetenstudien, VI Kernverschmelzungen. . . . Ber. d. Deut. 
Bot. Ges. 25 : 23-26. 1907. 



I02 



FUNGOUS DISEASES OF PLANTS 




Fig. 22. Flasmod/ophoka Brassicai: Si'ore, 
Germinating Spore, and Swarmspores 



a pulsating vacuole are always seen. Fig. 22 shows a spore and 
some swarmspore stages. Later, the protoplasmic mass moves 
wholly by amoeboidal streaming. It is believed that the swarm- 
spores may fuse into small amoeboidal plasmodia and that these may 
also gain entrance to the host. Nevertheless, the true plasmodial 

stage is apparently that 
which is developed im- 
mediately preceding 
spore formation. It has 
been noted that in the 
same cell the develop- 
ment of the spores is 
simultaneous, and this may be true also of a whole cell group 
(Krankheitsherde) occupying an area so large as to be visible to 
the unaided eye. So it would seem probable that we may look 
upon a Plasmodium as extending through a considerable mass of 
tissue. The mature spore possesses a refractive wall, or membrane, 
the contents are granular, and include some differentiated bodies, 
or globules, the nature of which has not been carefully determined. 
Control. On account of the fact that this parasite gains en- 
trance through the soil, numerous experiments have been made 
in the treatment of soils with lime, sulfur, and other fungicidal 
substances. In general it has been found that liming is the most 
reliable method of prevention, lime being applied to ordinary soils 
at the rate of about one hundred bushels per acre every few years. 
It is further \'cry important that all refuse from a previous crop 
should be destroyed. It is especially advisable that such refuse 
should not be thrown upon the compost heaps. Rotation of 
crops, with destruction of weeds which may harbor the parasite, 
should also receive attention. 



CHAPTER IX 

SCHIZOMYCETES. BACTERIA 

Chester, F. D. A Manual of Determinative Ijactcriology. 401 pp. /qo /i]i;s. 
MiGULA, W. System der Baktericn 1: 368 pp. 6 ph. 1S97; 2: 1069 pp. 

18 pis. 1900. 
Smith, Erw. F. Bacteria in Relation to Plant Diseases. Carnegie Inst, of 

Washington, Publication 27 (Vol. I): 285 pp. Ji pis. 14^ figs. 1905. 
Van Hall, J. J. Bijdragen tot dc kennis der Bakterieele Plantenziekten. 

197 pp. 1902. Amsterdam. 

The Schizomycetes, or fission fungi, better known as the 
bacteria, embrace numberless species of microorganisms which 
are, perhaps, morphologically the simplest of the fungi. These 
organisms consist of minute single cells, and while the cells 
may often be arranged in chains or filaments, loosely associated 
in colonies, or temporarily bound together in sheaths, there is 
no case in which an individual may be looked upon as more 
than a single cell. The cell forms of these organisms may be 
constantly assigned to one of only three general types, namely, 
spherical (Coccus type), rod-like (Bacillus type, varying from 
spheroidal to long rod-shape), and spiral (Spirillum type or screw 
form). The diameter of the cells of the coccus forms may vary 
from .3 to 3 /x (micromillimeters), and of other forms from 
.3-4 X 1-20 /A, the maximum being attained by the screw form. 
These organisms play an exceedingly important role in the econ- 
omy of nature. The great majority are saprophytic, }'ct many 
species induce diseases of animals. A relatively small number 
of species included in a single family (so far as present knowl- 
edge goes) produce diseases in plants. These diseases, however, 
rank among the most important both on account of the destruc- 
tive action of these organisms and the great difficulty experienced 
in attempting to develop effective means of control. The number 
of phytopathological forms is annually augmented, and it is proba- 
ble that they will be reckoned as relatively more important as 
further investigations are made. 

103 



I04 FUNGOUS DISEASES OF PLANTS 

Owing to the simple forms of these organisms, a thorough 
knowledge of the morphology of a species would not alone 
suffice, even roughly, to differentiate the numberless more or 
less similar species. Fortunately, the development of pure-culture 
methods has made possible a variety of tests, or points of com- 
parison. Growth characteristics of colonies, the reactions and 
products on numerous culture media, the thermal, photal, patho- 
logical, and other relations of the germ — in short, all physiolog- 
ical properties — must be studied and tabulated in order to make 
accurate and trustworthy comparisons. 

Recently a descriptive chart has been prepared for the Society 
of American Bacteriologists ^ which indicates concisely, yet com- 
pletely, the characters which should be carefully studied and tabu- 
lated in the case of any organism before it may be said that the 
organism may be fully and properly described. This chart should 
be in the hands of every student and would serve as a score card. 
In short, the description covers general morphology, cultural fea- 
tures, certain physical and biochemical characteristics, and patho- 
genic relations. Under morphology, size, form, and adherence of 
the vegetative cells are noted. The nature of the movement, the 
type of endospores, flagella, capsules, zooglcea, involution forms, 
and staining reactions should be followed. The cultural features 
include a complete discussion of agar, streak and stab cultures, and 
also cultures on potato, blood serum, gelatin, beef broth, milk or 
litmus milk, starch jelly, silicate jelly, a special study of the colo- 
nies on agar and gelatin, and the special growth reactions upon 
synthesized nutrient solutions. 

The physico-chemical features are concerned with the produc- 
tion of gases, acids, alkalis, alcohol, ferments, etc. ; the reduction 
of nitrates, or the presence of nitrites or nitrates in the culture ; 
indol-production, resistance toward acids, alkalis and other toxic 
agents ; vitality ; and temperature relations, particularly the thermal 
death point, the maximum, minimum, and optimum for growth. 

In the case of the pathogenic organisms, a complete study of 
infection, the relation of the organism to the legions produced, and 
special reaction of hosts and parasite should be considered. 

1 This chart was prepared by F. D. Chester, F. T. Gorham, and Erwin F. Smith, 
and was indorsed by the Society at its annual meeting, December 31, 1907. 



SCHIZOMYCETES. BACTERIA 



105 



This is accompanied by a numerical system for recording the 
sahent characters of an organism, as follows : 
100. Endospores produced 

200. . Endospores not produced 

10. Aerobic (strict) 

20. Facultative anaerobic 

30. Anaerobic (strict) 

1. Gelatin liquefied 

2. Gelatin not liquefied 

0.1 Acid and gas from dextrose 

0.2 Acid without gas from dextrose 

0.3 No acid from dextrose 

0.4 No growth with dextrose 

.01 Acid and gas from lactose 

.02 Acid without gas from lactose 

.03 No acid from lactose 

.04 No growth with lactose 

.00 r Acid and gas from saccharose 

.002 Acid without gas from saccharose 

No acid from saccharose 
No growth with saccharose 
Nitrates reduced with evolution of gas 
Nitrates not reduced 
Nitrates reduced without gas formation 
Fluorescent 
Violet chromogens 
Blue chromogens 
Green chromogens 
Yellow chromogens 
Orange chromogens 
Red chromogens 
Brown chromogens 
Pink chromogens 
Non-chromogenic 

Diastasic action on potato starch (strong) 
Diastasic action on potato starch (feeble) 
Diastasic action on potato starch (absent) 
Acid and gas from glycerin 
Acid without gas from glycerin 
No acid from glycerin 
No growth with glycerin 
ft lis (Pam.) Erw. Smith becomes Ps. 21 1.333151.) 
The bacteria are ordinarily grouped in six families, arranged in 
two orders, but the phytopathological forms are included in the 
one family Bacteriaceas. 



.003 
.004 
.0001 
.0002 
.0003 
.00001 
.00002 
.C0003 
.00004 
.00005 
.00006 
.00007 
.00008 
.oooog 
.00000 
.000001 
.000002 
.000003 
.0000001 
.0000002 
.0000003 
.0000004 
{Pseiidoiiionas caiiipc 



I06 FUNGOUS DISEASES OF PLANTS 

I. BACTERIACE^ 

These organisms consist of cylindrical or occasionally somewhat 
ovoidal rod-like cells, straight or very slightly curved, never spiral. 
Growth is by elongation of the rod, and division takes place by a 
septum (leading to a fission) perpendicular to the direction of elon- 
gation. Separation of the daughter cells may take place in such a 
way that the cells may commonly be single, or united two or more 
in a chain. Kndospores are frequent, rare, or wanting, depending 
upon the species. Motile organs (flagella) may or may not be 
present. 

The majority of the important plant disease-producing species 
thus far found are included in two genera, both of which possess 
motile organs,^ viz. Pseudomonas'^ and Bacillus. 

Pseudomonas Migula. These organisms are motile by means 
of flagella on one pole of the cell only, the flagella varying in 
number from i to lO, usually 1-3 (monotrichiate or lophotrichiate). 
Endospore formation is relatively rare. 

This is a rather comprehensive genus on account of the variability 
in the number of flagella, varying on the one hand towards Bacil- 
lus, and on the other, when the rods are slightly curved, toward 
Microspira of the spiral forms. Among species of special interest 
in this connection are the following : Psciniomouas cavipcstris 
(Pammcl) PLrw. Smith, Psaidouiotias Stcivarti Erw. Smith, Pscudo- 
vioiias PJiascoli Erw. Smith, Pscudouionas tuvicfaciois (P2rw. Smith 
and Townsend). Pseudomonas Olac (Arcan.) Trev., Pscndonionas 
Hyaciiithi (Wakker) P2rw. Smith, Pseudomonas vascularum (Cobb) 
Erw, Smith, Pseudomonas Juglandis Pierce, Pseudomonas mal- 
vaeeannn P>w. Smith, J^seudomonas Syfingtc \^.n Hall, and Pseudo- 
monas JVuni Erw. Smith may also be mentioned. 

Bacillus Cohn (emend.). These organisms are motile by means 
of wavy-bent flagella scattered irregularly over the cell (polytrichiate). 

1 A few species of the nonmotile genus Bacterium (Migula emend.) have been 
described as of phytopathological interest, among which are Bcicterium teiitliitm 
Metcalf. (Centrbl. f. Bakt. Parasit. u. Infektionskr. 13 (II. Abt.) : 2S-30. 1904; 
also Neb. Agl. Exp. Sta. Rept. 17 : 69-112. 1904.) 

2 Smith has advanced (Bacteria in Relation to Plant Diseases, pp. 16S-171) 
strong arguments for the substitution of Bacterium in place of Pseudomonas ; and 
he would establish a new generic name, Aplanobacter, for the nonmotile forms 
generally referred to Bacterium. 



SCHIZOMYCETES. BACTERIA 107 

The flagella in many species are relatively evanescent, or produced 
at a definite period, so that the time of motility may be brief. The 
cells are more commonly united into short threads than in the case 
of the preceding genus. Endospores are frequent. Among the 
species of much importance may be mentioned the following : 
Bacillus amylovorus Burrill, Bacilhcs tracJieipJiihis Erw. Smith, 
Bacillus caj'otovorus Jones, Bacillus aroidece Townsend, Bacillus 
solanacearujn Erw. Smith, Bacillus HyaciutJii-scpticus Heinz, 
Bacillus Ciiboniauus Macch. 

II. BLACK ROT OF CABBAGE 
Psendomouas campestris ( Pammel) Erw. Smith 

Garman, H. a Bacterial Disease of Cabbage. Ky. Agl. Exp. Sta. Rept. 3 : 

43-46. 1890. 
Hakdixg, H. a. Die schwarze Fiiulnis des Kohls und verwandter Pflanzen, 

eine in Europa weit verbreitete Pflanzenkrankheit. Centrbl. f. Bakt. Par- 
ask., u. Infektkr. 6(11. Abt.): 305-313. 1900. 
Harding, Stewart, Prucha. Vitality of the Cabbage Black Rot Germ on 

Cabbage Seed. N. Y. Agl. Exp. Sta. Built. 251 : 177-194. 1904. 
Pammel, L. H. Bacteriosis of Rutabaga {Baci/his campestris n. sp.). Iowa 

Agl. Exp. Sta. Built. 27: 130-135. pi. i. 1S95. 
Russell, H. L. A Bacterial Rot of Cabbage and Allied Plants. Wis. Agl. 

Exp. Sta. Built. 65: 1-39. fii^-^. 1-12. 1898. 
Smith, Erw. F. Centrbl. f. Bakt.Parask., u. Infektkr. 3(11. Abt.): 284-291, 

408-415, 478-486. pis. 1-6. 1897. 
Smith, Erw. F. The Black Rot of the Cabbage. U. S. Dept. Agl., Farmers' 

Bulk. 68: I -2 1. 1S98. 
Smith, Erw. F. The Effect of Black Rot on Turnips. U. S. Dept. Agl., 

Bureau of Plant Industry, Built. 29: 1-19. pis. 1-13. 1903. 
Stewart, F. C, and Harding, H. i\. Combating the Black Rot of Cabbage 

by the Removal of Affected Leaves. N. Y. Agl. Exp. Sta. Built. 232: 

43-65. pis. 1-2. 1904. 

Habitat relations. In recent years this cabbage disease has be- 
come well known as the most destructive and lea.st controllable 
cabbage disease. It has been very generally reported from the 
states of the Mississippi Valley and eastward, extending into 
Canada as well. It is also well known in Europe. Possibly a form 
of the same disease may occur in Japan upon radishes. 

It has been shown that infection takes place by way of the water 
pores of the host. In accordance with this fact, the climatic con- 
dition favoring the entrance of the organism is sufficient moisture 
in connection with warm days and cool nights. This would favor 



Io8 FUNGOUS DISEASES OF PLANTS 

the suffusion of the plant with water, and even the extrusion of 
droplets from the pores. Cool weather, warm, dry nights, and a 
dry soil offer a check to the disease. Smith's careful study of 
water pore infections has contributed greatly to our knowledge of 
the method of bacterial attack. 

Symptoms. The first symptoms in the leaves are manifested ^ 
" at the margins, and consist of yellowing of all the affected parts 
except the veins, which become decidedly brown or black [see 
Fig. 24]. The leaves appear to have ' burnt edges.' From the mar- 
gin of the leaf the progress of the disease is inward and downward 
through the stem. It usually enters the latter through the leaves. 




A B 

Fig. 23. Black Rot of Cabbage. (Photograph by F. C. Stewart) 
A, inoculated and diseased plant ; B, control, healthy 

Subsequently the disease passes out again from the infected stem 
into healthy leaves and up into the center of the head. If leaves 
diseased at the edges are pulled off and examined where they join 
the stem, the groups of fibrovascular bundles, or leaf traces, in the 
petiole, are seen to be either free from the disease, in the early 
stage, or decidedly brown or even deep black from its presence. 
Leaves attacked in this manner fall off prematurely one after 
another, leaving in bad cases a more or less elongated stem cov- 
ered with leaf scars and crowned with a tuft of small leaves. If 
the disease has entered the stem only on one side, that side is 
dwarfed and the head becomes one-sided." When young plants 

1 Smith. The Black Rot of the Cabbage, /. c, p. 6. 



SCHIZOMYCETES. BACTERIA 109 

are affected they may be killed. Any affected plants are prey to 
saprophytic organisms, and an offensive soft rot is then likely to 
result. Whether in the leaves or in the stem, the course of the 




Fig. 24. A Cabbage Leaf with Black Rot developing from Water 
Pore Infections. (Photograph by F. C. Stewart and H. A. Harding) 

disease may usually be traced by a darkening of the fibrovascular 
bundles. Fig. 23 shows a healthy and a diseased plant, the latter 
as a result of artificial infection. Root infection may also occur. 

This disease has been found upon apparently all of the common 
varieties of cabbage, in regions where the organism has gained a 
strong foothold. Turnips, cauliflower, kale, rape, and other species 



no 



FUNGOUS DISEASES OF PLANTS 



of cultivated and wild cruciferous plants (such as mustard and 
charlock) are also known to be susceptible. 

The organism, morphology and reactions. Upon gaining entrance 
through the water pores upon the margins of leaves this organism 
multiplies enormously. It is probable that a cellulose enzyme is 
slowly secreted, for in time masses of bacteria cause the progress- 
ive disappearance of the cell wall in contact with them. Through 
the vessels of the fibrovascular bundles they make most rapid ad- 
vances. Affected bundles are indeed usually chambered pure cul- 
tures of this organism, and poured plate cultures, with proper 
precautions, show a remarkable purity. Upon cutting such affected 




Fig. 25. A and />, Vascular Bundles from Turnip Root, showing Forma- 
tion OF Bacterial Cavity; C, The Bacteria. (After Erw. F. Smith) 

bundles the organism may ooze out in yellow droplets. In time 
practically any tissue of the host may be softened and disorganized 
(Fig. 25, ^ and B). 

The organism is a short rod, with a rather long flagellum (Fig. 
25 C). It is but slighdy longer than broad in the tissues of the host, 
yet in artificial culture it may be several times as long as broad, 
measuring 0.7-3.0 x 0.4-0. 5 /^. It is actively motile when young 
and nonmotile with age. It is commonly single or in pairs, and 
no spores have been found. It responds readily to stains. 

It grows well in slightly alkaline bouillon, developing turbidity 
and a yellow precipitate. Gelatin is gradually liquefied, complete in 
fifteen days at 17° to 19° C, with yellow precipitate. On feebly 



SCHIZOMYCETES. BACTERIA III 

alkaline agar (22° Fuller's scale) colonies are circular, pale to wax 
yellow in color, margin entire. On potato there is a copious, flood- 
ing growth, with no browning of the substratum, and no odor. No 
acid is produced. All liquid cultures become gradually alkaline. 

The optimum growth is believed to be at 25° to 30° C, and 
growth is feeble at 5° and 7° C, and at 37° and 38° C. It is killed 
by an exposure of ten minutes at 51° C. It differs from Psemio- 
nionas HyacintJii, to which it is related. 

It is believed that this organism is able to pass the winter in 
the soil of fields in which it has been abundant. The suggestion 
has also been made that it may be disseminated through compost 
when cabbage refuse has contributed to the compost heap. Re- 
cently it has been demonstrated that some of these germs are able 
to live over on the seed for at least a year. 

Control measures. The most dangerous sources of infection are 
the infested fields and the seed beds. Seed beds should be watched 
carefully, and no suspicious plants used. A rotation of crops is 
the sole means of eradicating the organism from a field once in- 
fested. Insects, snails, etc., may spread the disease to some extent. 
When leaves only have become infected, picking these and burn- 
ing them may be of service, although in most instances this method 
has proved a failure. Seed treatment (mercuric bichlorid i to 1000, 
fifteen minutes ; or formalin i to 200, twenty minutes) is advised. 

III. WILT OF SWEET CORN 
Pseudomonas Sfeituirti Erw. Smith 

Stewart, F. C. A Bacterial Disease of Sweet Corn. N. Y. Agl. Exp. Sta. 

Bulk. 130: 401-412. pis. 1-4. 1897. 
Smith, Erw. F. Notes on Stewart's Sweet-Corn Qje.xTc\.{Pseudomoiias sieivarii 

n. sp.). Proc. Am. Assoc. Adv. of Sci. 47: 422-426. 1898. 
Smith, Erw. F. U. S. Dept. Agl., Div. Veg. Phys. and Path. Built. 28: i- 

153. 1901. 

This disease was first discovered in the market gardens of Long 
Island, where much damage was done to sweet corn, Zca mays. 
It has since been found in Iowa and reported from parts of New 
York, so that it is doubtless widely spread. It is entirely distinct 
from the disease of field corn described by Burrill.^ 

1 Burrill, T. J. A Bacterial Disease of Corn. 111. Agl. Exp. Sta. Built. 6 : 
165-176. 1889. 



112 



FUNGOUS DISEASES OF PLANTS 









Symptoms. The external and internal symptoms of this disease 
are readily noted and distinctive. The affected plants die by wilt- 
ing and drying, the water supply being cut off. Usually the leaves 
wilt one after another and the plant may live a month, but in some 

cases where the plants affected 
are a foot or less in height si- 
multaneous wilting of the leaves 
may result, and the plants may 
die within four or five days 
of the first appearance of the 
disease. There is no discolora- 
tion, decay, or other complicat- 
ing symptoms. 

The internal evidence of dis- 
ease is equally clear. Upon cut- 
ting the stem lengthwise, the 
" fibro vascular-bundles appear," 
according to Stewart, " as yel- 
FiG. 26.^Cross Section^of Stalk of low streaks in the white paren- 
chyma ; but in the stems of 
plants that have been dead for 
some time some of the bundles 
may be black instead of yellow. If the stem is cut crosswise and 
the cut surface exposed to the air for about five munutes, a yellow 
viscid substance exudes in drops from the ends of the vessels." 
Except for the greater accuracy of poured plates, pure cultures, 
which are essential, might be made by direct inoculation into tubes. 
The appearance of diseased bundles in cross and longitudinal sec- 
tions is illustrated in Figs, 26 and 27. 

Pathology. The organism is confined to the fibrovascular bun- 
dles exclusively, and appears to infest only the vessels. There is 
no disorganization of the tissue, and the pathological effect is there- 
fore due, in large part, doubtless, to cutting off the transpiration 
stream. If there are secondary effects felt in the protoplasm of 
rather distant living cells, and brought about by diffusion of inju- 
rious excreted substances, it has not been demonstrated, so far as 
I am aware, in the case of any bacterial disease of plants. Field 
corn and pop-corn are resistant, but inoculation experiments with 



Sweet Corn, showing Bundles occu 

PIED BY Bacterial Colonies. (Photo 

graph by F. C. Stewart) 



SCHIZOMYCETES. BACTERIA 



113 



sweet corn have been successful. The organism is probably spread 
by many mechanical agencies, and also distributed clinging to the 
seed. 

The organism, morphology and reactions. The rods arc short, 
almost ovoidal in form, ordinarily 1.3-1.6 x .7-.8/A. On agar 
the colonies are more or less circular, becoming lobulated at the 
margins. With age the surface is granular. The color changes 
from yellowish white to bright yellow. Gelatin is not liquefied. A 




Fig. 27. LuNGiTuuiNAL Section of Stalk of Sweet Corn, 
SHOWING A Diseased Bundle. (Photograph by F. C. Stewart) 



vigorous growth is produced on steamed potato, which in a week 
is iridescent. The potato turns brown in time. 

In bouillon a turbidity is produced, and gradually a yellowish- 
white precipitate is formed. Yellow, surface-colony globules appear. 
In Uschinsky's solution there is a vigorous growth, litmus milk is 
slowly decolorized, and there is no coagulation. Gas is not pro- 
duced, and the organism is aerobic and facultative anaerobic. 

Control measures. There is great difference in the susceptibility 
of varieties of sweet corn, and this may be made use of where 
necessary. Only sound seed from uninfested regions should be 
employed. A rotation of crops is also an important precautionary 
measure. 



114 FUNGOUS DISEASES OF PLANTS 

IV. CROWN GALL OF APPLE, PEACH, AND OTHER PLANTS 
Pseudomoiias tumefaciens Erw. Smith and Townsend ^ 

Hedgcock, Geo. G. Crown Gall, Hairy Root Disease of the Apple. Bureau 

Plant Industry, U.S. Dept. Agl. Built. 90 (Pt. II): 15-17. pis. j-j. 

1906. 
Hedgcock, Geo. G. The Cross Inoculation of Fruit Trees and Shrubs with 

Crown Gall. Bureau Plant Industry, U. S. Dept. Agl. Built. 131 (Pt. Ill): 

21-22. 1908. 
ScHRENK, H. VON, and Hedgcock, Geo. G. The Wrapping of Apple Grafts 

and its Relation to Crown Gall Disease. Bureau Plant Industry, U. S. 

Dept. Agl. Built. 100 (Pt. II): 5-12. 1906. 
Selby, a. D. Diseases of the Peach. Ohio Agl. Expt. Sta. Built. 92 : 208- 

217. pis. j~6. 1898. 
Smith, Erw. F., and Townsend, C. O. A Plant Tumor of Bacterial Origin. 

Science, N. S. 25: 671-673. 1907. 
TOUMEY, J. W. An Inquiry into the Cause and Nature of Crown Gall. Ariz. 

Agl. Exp. Sta. Built. 33: 1-64. Jigs. 1-31. 1900. 
Townsend, C. O. A Bacterial Gall of the Daisy and its Relation to Gall 

Formations on Other Plants. Science, N. S. (Abstract) 29: 273. 1909. 

Occurrence. The crown gall has thus far been found most 
commonly upon rosaceous plants (Rosaceas), among these being 
included practically all of the stone, pomaceous, and bush fruits 
of this family, especially the various species of Prunus, Pyrus, 
Rubus, and Rosa, It has, however, been reported upon a variety 
of other plants, such as the grape {Vitis spp.), walnut {Jiiglatis 
Jiigi'o), chestnut {Castanea dejitatd), poplar {Popiibis alba), willow 
{Salix), etc. Thus far, very little striking varietal resistance has 
been reported, although it is probable that the almost total absence 
of the disease under certain conditions is to be attributed in part 
to the difference in the susceptibility of the hosts as well as to 
diversity of external conditions. In general, nursery stock is 
more readily affected than older trees ; but this may be due to 
greater opportunity for infection. 

1 It seems justifiable to give as conclusive the evidence thus far presented re- 
garding the bacterial nature of the widespread crown gall. This evidence has been 
published by Smith and Townsend only as a preliminary paper and as abstracts of 
reports (one cited in the literature above) read before two societies at the meeting of 
the American Association for the Advancement of .Science, and Affiliated Societies, 
Baltimore, December, 1908. The data and proofs orally presented, however, leave 
no reasonable doubt as to the bacterial cause of a large number of gall formations. 
It is not yet clear whether the galls of all such plants as apple, peach, grape, etc., 
are due to the particular species here described, or to closely related species. This, 
however, is a matter of far less present significance. 



SCHIZOMYCETES. BACTERIA 115 

Upon different hosts the galls differ only slightly in form and 
appearance. Moreover, they are generally located near the sur- 
face of the soil in the region of the collar. A gall may, however, 
develop above the surface, or at some distance below, upon the 
smaller roots. Superficial galls are more common where the ex- 
posed portions are subject to such injuries as those produced by 
rodents or the implements used in cultivation. 

Development of the gall. Published results regarding the de- 
velopment of these galls are based upon an examination of woody 
plants. It is probable that important differences will be found in 
the case of herbaceous plants. In general, the gall is an annual 
structure, even on woody plants, beginning its growth with ex- 
foliation in the spring and maturing more or less by the time of 
leaf fall. When first observed the hypertrophies are small masses 
of rapidly growing, almost translucent tissue, nearly spherical in 
shape. According to Toumey, such galls, when developed super- 
ficially in cultures, may become greenish from the presence of" 
chlorophyll. In any event, the clear white appearance is lost in 
a few months and the gall becomes warty and browned. During 
the latter part of the season, or during the winter, disintegration 
results, apparently by a normal process of decay. As a rule, such 
galls do not develop secondary galls from any portion of the old 
part but are entirely destroyed. Young galls may, however, spring 
from the collar or roots near the margin of the gall previously 
formed, and thus the wounds and injurious effects are intensified 
from year to year. In time the functions of the conducting 
tissues are so interfered with that death of the parts above follows 
gradually. In the South and Southwest, galls which begin to grow 
rather late in the season may continue their growth throughout 
another year. 

According to Toumey " when the gall first begins its develop- 
ment, there is a pushing outward of a small area of the true 
cambium, which is transformed into large hypertrophied paren- 
chyma cells. ... In its youngest stages the tissue of the gall 
is a mass of parenchyma with numerous minute areas of rapidly 
dividing meristem scattered through it. The areas of meristematic 
tissue are centers of growth. . . . As the galls become older 
these centers of growth increase in size and others originate in 



ii6 



FUNGOUS DISEASES OF PLANTS 




Fig. 28. Crown Gall of Peach 



the newly formed parenchyma. The centers of these growths ulti- 
mately become most curiously twisted nodules of tracheides and 
woody fibers." 

Galls upon relatively small roots may not attain more than 
a centimeter in diameter, while ordinarily on nursery stock, 

raspberries, etc., they may be as 
large as a walnut (Fig. 28). On 
the crowns of large trees they 
may be much larger. 

Cross-inoculation experiments. 
It has cost no small amount of 
effort to determine the cause 
of crown gall. Toumey found 
a Myxomycete developing occa- 
sionally upon the cut surfaces of 
galls in impure cultures. He 
further observed appearances of 
the protoplasm in certain cells of the parenchyma of young galls 
suggesting stages in the development of the plasmodia. The evi- 
dence was not strong, however, and many pathologists reserved 
a final opinion regarding the nature of this disease. It was long 
apparent that the disease is infectious, and many experiments 
demonstrated that it could be conveyed from one susceptible 
plant to another by inoculation of the roots with macerated galls 
or by burying infected parts of diseased plants in the vicinity of 
healthy roots. The results of rather recent and extensive inocula- 
tion experiments by Hedgcock are summarized by him as follows : 
" The soft galls from the almond, apricot, blackberry, cherry, 
peach, plum, prune, and raspberry have been transferred easily 
to seedlings of the almond, apricot, peach, and raspberry ; less 
readily to those of the blackberry, cherry, plum, prune, and pear ; 
and with great difficulty to seedlings of the apple, chestnut, wal- 
nut, and rose. 

" The soft galls of the apple, chestnut, walnut, rose, and pear, 
as a rule, have not been transferred readily to any of the plants 
mentioned. Evidence has been obtained of a wide range of suscep- 
tibility in different varieties of the same plant. This has been noted 
in varieties of the apple, blackberry, cherry, chestnut, pear, and rose. 



SCHI7X)MYCETES. BACTERIA 



117 



" The results of these experiments show that the opportunity 
presented for breeding and selecting races of plants resistant to 
this common and destructive disease is excellent." 

Abundant, substantial proof has now been brought forward by 
Smith and Townsend demonstrating the bacterial nature of this 
disease. This work resulted from an examination of galls appear- 
ing naturally upon the Paris daisy, ChrysantJicmuvi fnitcsccns. 
From the last-named plant they were able to isolate a species of 
bacteria which proved to be pathogenic. They reported in 1907 
more than three hundred successful inoculations under different 
conditions. In at least two series of experiments 100 per cent of 
the inoculations were effective, control plants remaining wholly 
free from galls under similar conditions. The organism was then 
described as Bacterium tiDnefacicns. It produces hypertrophies 
very readily in young tissues, particularly in fleshy organs, and 
it sometimes induces abnormal growths on the wounded parts 
of young cuttings. This organism was found to affect, with more 
or less similar lesions, many plants, including the tomato, tobacco, 
potato, sugar beet, grape, carnation, raspberry, peach, and apple. In 
four or five days after inoculation, swellings were evident, the latter 
on the daisy attaining an inch in diameter after a month or more. 

According to Townsend, "this work has led to the isolation of 
pathogenic Schizomycetes from the galls of peach, hard galls of 
apple, hairy root of apple, hop, rose, and chestnut. The organisms 
obtained from the galls of these different plants are cross inocula- 
ble and are very similar, if not identical in size, shape, structure, 
and habits of growth on media with the organism from the daisy 
gall." It is further ascertained that galls produced by the daisy 
organism are very similar" to those formed by the organism from 
the woody plants. It is apparent that it is too early to expect 
definite evidence as to the occurrence of biological forms or other 
more accentuated differences. 

The organism. This species has already been studied with 
respect to its reactions on various media, and it is described as 
a short rod, motile by from one to three flagella. Cultivated 
on agar the translucent white, round colonies appear slowly at 
25° C. The margins are smooth and dense. It produces no gas. 
Bouillon is not heavily clouded, and gelatin is not liquefied. The 



Il8 FUNGOUS DISEASES OF PLANTS 

organism grows very slowly at blood heat, but shows some growth 
at o° C. 

Control. It has been found very difficult effectively to cure 
trees upon which the gall has appeared. Removal of the gall 
with the tissues adjacent thereto, and the use of antiseptic 
washes, do not insure the complete isolation of the disease. It 
is evident, therefore, that there is difficulty in removing all dis- 
eased tissues. Since the gall develops promptly in nursery stock, 
it is readily detected at the time of transplanting, and such in- 
fected stock will, wherever possible, be discarded. Any injuries 
to growing trees at or near the surface of the ground will make 
infection easier, and consequently care should be taken in the 
cultivation of orchards. 

V. OLIVE KNOT, OR TUBERCLE-DISEASE OF THE OLIVE 
Pseudomofias Olece (Arc.) Trev. 

Petri, L. Untersuchungen iiber die Identitrit des Rotzbacillus des Oelbaumes. 

Centrbl. f. Bakt., Parask., u. Infektkr. 19 (Abt. II): 531-538. 1907. 
Pierce, N. B. Tuberculosis of the Olive. Journ. Myc. 6: 148-153. pis. 14- 

15. 1 89 1. 
Savastano, L. Tuberculosi, iperplasie e tumori dell' olive. I e II Memoria, 

Ann. d. R. Scuola Sup. d'Agr. in Portici 5: 131 pp. 1887. 
Smith, C. O. A Bacterial t)isease of Oleander. Bot. Gaz. 42 : 301-310. 1906. 
Smith, Erw. F. Recent Studies of the Olive-Tubercle Organism. Bureau 

Plant Industry, U. S. Dept. Agl. Built. 131 : 25-43. iQoS. 

The olive knot was known in early times. It is not uncom- 
mon throughout the Mediterranean region, but it is perhaps 
most abundant in Italy. It seems to occur also in California. 
The knot is conspicuous from the development upon the smaller 
twigs and branches of a knob or tuberculate swelling. Small 
swellings may also occur on the leaves. The formation of the 
tubercle usually begins in the spring, and where the tubercle 
surrounds the branch the latter suffers considerable injury, and 
may eventually die. 

Inoculation experiments made with pure cultures of the iso- 
lated organism have yielded characteristic infections, both in the 
experiments reported by Italian investigators and in those of 
Erwin Smith ^ in the United States. C. O. Smith has studied 

^ Smith, Erwin F. Bacteria in Relation to Plant Diseases 1 : 10. 



SCHIZOMYCETES. BACTERIA 



119 



a bacterial disease of the oleander in California, and from cul- 
tural characters of the organism isolated, as well as from inocula- 
tion experiments, he considers this organism to be Psciidouioiias 
Olccc. On the other hand, Erwin Smith would regard this as 
improbable, since he obtained no infections on oleander. He 
would seem to suggest that the organism isolated in California 
may have been the organism of crown gall (see p. 114). 

VI. BEAN BLIGHT 
Psciidomonas Fhaseoli Erw. Smith 

Beach, S. A. Bean Blight. N. Y. Agl. Exp. Sta. Rept. 11 : 553-555. 1892. 

Smith, Erw. F.- Description of Bacillus Fhaseoli, n. sp. Proc. Am. Assn. 
Adv. Sci. 46: 288-290. 1897. 

Smith, Erw. F. The Cultural Characters of Four One-Flagellate Yellow Bac- 
teria Parasitic on Plants. U. S. Dept. Agl., Div. Veg. Phys. and Path. 
Built. 28 : 1-153. 1901- 

Whetzel, H. H. Some Diseases of Beans. Cornell Agl. Exp. Sta. Built. 
239: 197-214. Jigs. loo-i i§. 1906. 

The bean blight, a disease far more common and destructive 
in the United States than has been generally believed, \:> due to 
this organism. The disease is common 
upon field, garden, and lima beans. It 
affects leaves, stems, and pods, but par- 
ticularly the leaves and pods, upon which 
the symptoms are also most conspicuous. 
It is believed that diseased seed is the 
source of many early infections, whereas 
later infections may result through wounds 
in any green parts. On the foliage there 
appear irregular water-soaked patches, 

which later become, during dry weather, FJ<-- -9- Psludomonas 
1 1 T-i J- Phaseoli 'Ek\n. Smith 

brown and papery. The disease pro- ,.., „ • t^ c- • 1-^ 

t^ t- J ^ I (After Erwm F. Smith) 

gresses slowly, therefore it becomes evi- 
dent, as a rule, only when the pods begin to form. Control is 
difficult, and must concern itself largely with seed selection 
and crop rotation. Seed from an affected field should not be 
planted. It is not enough to attempt to sort out healthy seed, 
when some of the lot are evidently diseased, for many which 
show no discoloration will be penetrated by the bacteria. 




I20 FUNGOUS DISEASES OF PLANTS 

VII. HYACINTH DISEASE 
Pseudomonas Hyacinthi (Wakker) Erw. Smith 

Smith, Erw, F. Wakker's Hyacinth Germ Pseiidoj/io/ias /ivcJci/it/ii (WBkk.er). 

U. S. Dept. Agl, Div. of Veg. Phys. and Path. Built. 26: 1-45. pi. i. 

Ibid. Built. 28 : 1-153. 1901. 
Wakker, J. H. Vorlaufige Mitth. iiber Hyacinthenkrankheiten. Bot. Centrbl. 

14: 315-317- 1883. 
Wakker, J. H. Onderzoek der Ziekten van Hyacinthen, en andere bol-en 

Knolgewassen (1884): 4-13. 

This organism, apparently confined to the Netherlands, is 
related to the three already discussed, yet it is entirely distinct. 
It produces a disease of hyacinths, entering the host through 
wounds or through the nectaries. The vascular system is chiefly 
affected, but the neighboring parenchymatous tissue is gradually 
involved, the middle lamellae being the first portions of the walls 
to succumb. The organism may require a year in which to destroy 
the host. 

VIH. BUNDLE BLIGHT OF SUGAR CANE 

Pseudomonas vascnlanim (Cobb) Erw. Smith 

Cobb, N. A. Diseases of the Sugar Cane. New So. Wales Dept. Agl. (1893) : 
I -2 1. 

Smith, Erw. F. Ursache der Cobb'schen Krankheit. des Zuckerrohrs. Cen- 
trbl. f. Bakt. Parasitenk. u. Infektionskr. 13 (II Abt.): 726-729. 1905. 

This organism is the cause of a disease of the sugar cane. 
It is not uncommon in Australia, and probably also in Java, 
Brazil, and other tropical countries. The organism attacks the 
fibrovascular bundles, — the etiology of the disease is not unlike 
that of Pscjidomonas Stezvarti Erw. Smith, — and a constant 
symptom is the excessive developmeni; in the bundles of a yellow 
gum. 

IX. PSEUDOMONAS: OTHER SPECIES 

Among other phytopathological species of special importance 
in certiiin regions, yet less well known, or imperfectly reported 
upon, are the following : 

Pseudomonas Juglandis Pierce is a parasite of the English or 
Persian walnut {Juglans rcgia) in California. ^-^ Young nuts and 
shoots are affected, and the disease is one of much importance. 

1 Pierce, N. B. Walnut Bacteriosis. Bot. Gaz. 31 : 272-273. 1901. 

2 Smith, R. E. Report of the Plant Pathologist to July i, 1906. Calif. Agl. Exp. 
Sta. Built. 184: 232-236. figs. 2-4. 1907. 



SCHIZOMYCETES. BACTERIA 



121 



Pseudomonas malvacearum luw. Smith. This parasite produces, 
through stomatal infections, water-soaked, angular areas (Fig. 30), 
known as angular leaf spot of cotton (Gossypium). Later these 




Fig. 30. Angular Leak Srui of Cotton. (Photograph by Erwin F. Smith) 



spots turn purple and finally become dry and brown. The disease 
is apparently widely distributed in the southern states, but the 
organism has not yet been fully described. ^ 

X. PEAR BLIGHT 
Bacillus (Vnylovonis (Burrill) De Toni 

Arthur, J. C. Diseases of the Pear. N. Y. Agl. Exp. Sta. Rcpt. 3 : 357-367- 

1884. 
Arthur, J. C. Histology and Biology of Pear Blight. Proc. Phil. Acad. Nat. 

Sci. (1886): 322-341. pi. 3. 
Burrill, T. J. Trans. 111. State Hort. Soc. (1877): 114; ibid. (1878): 80. 
Burrill, T. J. Proc. Am. Assn. Adv. Sci. 29: 583. 1880. 

1 Smith, Erw. F. Bacteria in Relation to Plant Diseases 1 : 95, 126. 



122 



FUNGOUS DISEASES OF PLANTS 



BuRRiLL, T. J. Anthrax of Fruit Trees; or the so-called Fire Blight of Pear, 

or Twig Blight of Apple Trees. 111. Indus. Univ. Kept. 10 : 583-597. 
Jones, L. R. Studies upon Plum Blight. Centrbl. f. Bakt. Paras, u. Infek- 

tionskr. 9 (Abt. II): 835-841. 1902. 
Waite, M. B. Cause and Prevention of Pear Blight. Year Book U. S. Dept. 

Agl. (1895): 295-300. 
Waite, M. B. Pear Blight and its Control in California. State Hort. Com. 

of Calif. (Special Report) (1906): r-20. 
Whetzel, H. H. The Blight Canker of Apple Trees. Cornell Univ. Agl. 

Exp. Sta. Built. 236: 103-138. Jij^'s. jo-Sj. 1907. 

Pear blight has been known in the United States for more than a 
century. Various common names have since been appHed to this 

disease, determined largely 
by the host plant upon which 
it was found, and by the par- 
ticular effect produced upon 
the host. Such names there- 
fore as fire blight, twig blight, 
blossom blight, and other 
more or less similar designa- 
tions have been applied. 

Geographical. This disease 
was first reported from the 
northeastern United States, 
but its occurrence was subse- 
quently established in states 
to the south, west, and south- 
west, and by 1878 it was evi- 
dently very well established 
throughout the United States 
east of the Mississippi. Still 
later it became an important 
bacterial disease in the far 
West and Southwest. It is certainly distributed throughout the 
United States at present, but so far as is known, it does not 
occur in Europe or in Asia. There is every indication that the 
disease had its original home in the eastern United States, and its 
original host was doubtless some species of crab apple or thorn tree. 
Its gradual spread westward, therefore, was governed by the spread 
of civilization and the consequent greater contiguity of orchards. 




Fig. 31. Tear Tree Practically Dead 

FROM Severe Attack of Pear Blight 

(Photograph by H. 11. Whetzel) 



SCHIZOMYCETES. BACTERIA 1 23 

Host plants. This species has received the name of pear Wight 
on account of the fact that it is a more disastrous and more com- 
mon disease upon the pear {Pyrus amimniiis) than upon any other 
of its numerous hosts. It is also found as a parasite of the 
2lYi^\q {Pyrus Mains), quince {Cydotiia vulgaris), and of numerous 
species of native pomaceous plants, such as wild crabs (Pyrus) 
and hawthorn (Crataegus), and recently it has been found on the 
plum. There is considerable difference in the susceptibility of 
the various varieties of pears. The growing of Bartlett and 
many other desirable varieties of our common pears in the south- 
ern states and in the Mississippi Valley has been very largely 
given up on account of the destructiveness of this disease. Such 
varieties as the Bartlett, Seckel, and Le Conte are much more 
susceptible, at least in most sections of the country, than such 
as the Kieffer, Duchess, and Winter Nelis. The Oriental group 
in general is more resistant, although the several varieties are by 
no means free from the disease under conditions favorable for its 
development and propagation. 

The pear blight is also a serious disease on apples, and there 
seems to be less difference in resistance among these fruits ; 
nearly all of the standard varieties being more or less affected. 

Symptoms. The pear blight is more commonly noticed during 
the early part of the season, when it appears in the form of twig 
blight throughout the blossoming period of both pears and apples. 
From two weeks to one month after the period of pollination the 
blossoms and tips may begin to wilt and show signs of general 
blackening, resulting finally in the complete blackening and death 
of all branches or spurs upon which flower clusters have been 
borne. In some instances scarcely a flower tija upon an infested 
tree is free from this general attack. As a matter of fact, the in- 
fection usually takes place at the time of blossoming and the dis- 
ease is most abundantly distributed at that time, as will be shown 
later. Upon the pear the blight may continue to extend down the 
twig or the branch, the branch being entirely killed as it progresses ; 
and in the course of some months it may have extended into the 
larger limbs, or into the main body of the tree (Fig. 31). Water 
shoots may also be affected both in the case of the pear and the 
apple (Fig. 32), and direct entrance to the body gained after a 



124 



FUNGOUS DISEASES OF PLANTS 



very short period of growth. Nevertheless, under conditions 
more favorable for the host plant the blight may never extend 
more than a few inches, resulting merely in a tip pruning. In 
the case of the apple this twig blight is the rule, the disease 
apparently being usually unable to maintain itself in the larger 
branches. Young fruits of the apple, an inch in diameter, are 




Fig. 32. Water Sprouts of Apple killed by Blight 

frequently affected ; and the copious growth of the organism 
gorges the fruit with the slime which may be exuded in droplets. 
The progress of the disease is ordinarily very clearly indicated 
by the appearance of the bark. The growth of the organism 
within the tissues of the soft bark causes a water-soaked appear- 
ance, and finally a blackening and shriveling. The organism 
may, however, extend to a distance of several inches, or even 
a foot, below the water-soaked area. When the organism ceases 
to spread rapidly in the tissues, a sharp line of demarcatioii is 
noticeable, separating the dead from the healthy or comparatively 



SCHIZOMYCETES. BACTERIA 1 25 

healthy tissues. In many instances the bark is broken, due proba- 
bly to a gelatinizing process set up by the organism in the tissues 
of the host ; and from these ruptured areas there are exuded beads 
of a gelatinous or gummy nature, varying in color from milky 
white to brown or black. In order to secure cultures when the 
disease is not very active, it will be found desirable to bring 
affected twigs into the laboratory, placing them under a bell glass 
with the basal ends in a vessel of water. 

The organism. The general life history of Bacillus amylovonis 
upon its host has become a landmark in our knowledge of bac- 
terial diseases. The relations of this organism to the disease have 
been under constant observation for about thirty years. The true 
cause of the disease was first suspected in 1877 (Burrill), and the 
final discovery that pear blight is due to a species of bacteria was 
of unusual significance, as it shared with the discovery made by a 
Dutch botanist (Wakker) the honor of constituting the pioneer 
work with bacteria from a phytopathological standpoint. 

The most careful observations and experiments indicate that 
the chief source of infection is by means of the visits of insects, 
especially bees, to the blossoms. The infection occurs, therefore, 
at the time of pollination. The bacillus multiplies very rapidly in 
the nectary of the flower, in which germs are directly inoculated 
by the visits of the insects. The rapid growth of the organism is 
such that after being inoculated into a blossom, and multiplying 
therein for twenty-four hours, it might be spread during the next 
day to many thousands of blossoms. From the nectary it gains 
entrance into the softer tissues of the bark and cambium, where 
it is very largely confined. Nevertheless, it is also true that in- 
fection may result through the growing twigs. Biting or piercing 
insects are doubtless of much importance in spreading the disease 
in this way. Injuries and sometimes, perhaps, even water pores 
may be the seats of infection. In general, however, it is certainly 
true that the presence of germs upon the surface of healthy tissues 
would not result in the production of disease in those parts. 

The bacillus winters over, under favorable conditions, in rela- 
tively few affected branches, under conditions where moisture 
is sufficient and protection from drying out adequate. It is from 
such wintered-over areas as centers that the disease is spread to 



126 



FUNGOUS DISEASES OF PLANTS 



the blossoms the following spring. With the return of growing 
conditions, fermentation may be set up and beads of the gummy 
exudation produced. Since the beads contain countless quantities 
of the bacillus, insects readily spread it to some blossoms ; thence 
it is promptly carried by bees to greater distances. The organism. 




P^iG. 33. Pear Fruit infested with the Blight Organism; Beads 
EXUDED IN Moist Chamber. (Photograph by H. H. Whetzel) 

however, is not very resistant to conditions. It is killed by very 
brief exposure to sunlight and by a period of drying. This latter, 
however, seems remarkable, in view of the general experience that 
no amount of cold can act unfavorably upon this organism. It is 
possible, however, that the effect of cold in the absence of mois- 
ture may be as disastrous as drying out. 

The characteristics of this organism according to Whetzel are 
as follows : 




SCHIZOMYCETES. BACTERIA I 27 

Single cells of the organism direct from the tree are oval, 1.5 
to 2 fjb long, and somewhat more than half as broad (F'ig. 34). 
They occur single or attached, several end to end. Upon various 
culture media they are more commonly single or in pairs, al- 
though sometimes in short threads, and in 
all cases motile in fresh cultures. 

On gelatin growth is slow, requiring three 
to five days for the appearance of colonies, 
the latter being globose to lenticular, yellow- 
ish, liquefying the medium very slowly. 

On agar the surface colonies appear more 
rapidly, being evident the second day, and fig. 34. Bacillus amy- 
attaining a diameter of from 2 to 3 mm. by lovorus from Apple 
the fourth or fifth day. They are white and Fruit; Simple Stain 
granular, or cloudy, with a sharply defined white center ; the mar- 
gins are entire or slightly wavy, with a dense white center. Immersed 
colonies are globose or lens-shaped, and opaque-yellowish. 

In bouillon a cloudiness is produced after twenty-four hours, 
and this is accompanied by slight acidity ; after forty-eight hours 
there is greater cloudiness, with more or less persistent flocci, 
the medium becoming alkaline, and in time showing a tendency 
to clear. In sugar-free bouillon the liquid remains clear for 
twenty-four hours, except for slight sediment. It is neutral at 
first, becoming cloudy and alkaline after some days. In milk 
no change is evident until the third or fourth day, when thick- 
ening begins, which increases to fifth or sixth day. The product 
finally becomes subgelatinous, and in ten days there is a clear 
liquid above. This is at first acid, becoming slightly alkaline. 
Litmus milk is unchanged. 

On slanting agar tubes growth in twenty-fouK hours is moderate, 
opalescent, spreading slowly, producing turpidity in the water of 
condensation ; growth not viscid. 

On gelatin stab cultures growth is similarly slow, and beaded 
or granular along the needle path ; surface growth with irregular 
or erose margin, center thin and granulose ; liquefaction slow, 
crateriform and stratiform. 

Control. The control of pear blight was for a long time con- 
sidered impossible, but careful study under various conditions 



128 



FUNGOUS DISEASES OF PLANTS 



(particularly the work of Waite) has shown that this disease 
may be controlled or even practically eradicated in large regions. 
The essential step consists in pruning out the blight in situations 
where it may winter over. If all of the blight could be thoroughly 
pruned out of the orchard during the fall and winter, there would 




Fu;. 35. Blight Canker on Trunk of Apple, from Infected Prun- 
ing Knife. (Photograph by H. 11. Whetzel) 

probably be no opportunity for infection the following season, ex- 
cept from distant orchards. In practice the pruning out of the 
blight during winter is not an easy process, and it requires 
the greatest care and keenest eyesight. It would be necessary 
to go over the orchard several times, the final observation being 
made only a short time before the opening of the blossoms. 



SCHIZOMYCETES. BACTERIA 1 29 

Pruning during the growing season is also practiced, but it is less 
reliable. Such pruning has not proven a great success on account 
of the fact that infection may be constantly taking place. More- 
over, when the blight is rapidly extending in a limb or trunk, it 
is difficult to determine the extent of the region affected. In deal- 
ing with this organism, in general, all possible bacteriological pre- 
cautions must be taken. Carelessness in the pruning of nursery 
stock may actually result in spreading the disease to practically 
all of the young trees. The knife should be promptly applied 
wherever a limb or trunk may be saved, and antiseptic precau- 
tions should be taken. 

XI. WILT OF CUCURBITS 

Bacillus tracheiphiliis Erw. Smith 

Smith, Erw. F. Bacillus tracheiphilus, sp. nov., die Ursache des Verwelkens 
verschiedener Cucurbitaceen. Centrbl. f. Bakt., Parasitenk. u. Infektskr. 
l(Abt. II): 364-373- 1895- 

The wilt of cucurbits was first reported about 1893 (Smith) and 
it is now the most common and perhaps the most serious disease 
among cucurbitaceous plants in the United States. It was at first 
known (to pathologists at least) in the northeastern states, but it 
is now common upon several hosts in Missouri, Colorado, and 
other western states. Cucumbers and melons would seem to be 
most susceptible, although pumpkins and squash may be attacked. 
Weather conditions do not seem to affect materially the abun- 
dance of this disease. 

Symptoms. The general symptoms are simple and striking. 
These consist of a progressive wilting of the host. If infection 
takes place upon the central stem, the wilting in the whole vine 
follows promptly. If, however, infection is in the distal parts of 
branches, there is gradual wilting back to the main stem. Then 
the remaining branches promptly show the effect. In the tissues 
there is at the time of wilting very slight, if any, evidence of a 
change in appearance. In no case is there the development of 
odors, or of decay in the usual sense. 

Infection and spread of the disease appears to result almost 
wholly through biting insects. The organism is found massed 
primarily in the vessels of the xylem. At first the spiral vessels 



I30 



FUNGOUS DISEASES OF PLANTS 



are the seat of action, and later the pitted vessels are infested. 
In late stages of the disease the lesions may be considerable, the 
bundle system being broken down and cavities formed in the ad- 
jacent tissues. The lesions are also very noticeable when the 
organism has gained entrance to the fruit. 

The organism is a rod averaging two or three times as long 
as broad, 1.2-2.5 X -S--/? often adhering in twos, and rapidly 
motile only when young (Fig. 37). The rods are readily stained 




^'V 










KiG. 30. Dacterial Wilt of Mf.lo.xs. (I'hotograph by II. H. Whetzel) 

with carbol fuchsin, but the flagella are not so readily demon- 
strated. Growth in bouillon results in a turbidity, and in potato 
decoction viscosity is developed with age. Coagulation of milk 
does not occur, and after weeks no viscosity is evident. On 
gelatin growth is slow, and there is no liquefaction. Similarly, 
on agar the clear, or milk-white, colonies spread slowly. Stab 
cultures develop a slight growth throughout the extent of the 
stab, with lobulated projections. On slices of potato there is a 




SCHIZOMYCETES. BACTERIA 131 

vigorous gray-white film, and no changes are manifest in the 
substratum. The organism is aerobic and perhaps facultative 
anaerobic. There is no gas production. 

The contents of the vessels affected are slightly alkaline, and 
alkaline media are apparently preferred. This organism is sensi- 
tive to high temperatures, 43° C. or over 
being fatal in ten minutes. Death results in 
fifteen minutes in dry air, and the normal 
life of a culture is from a few weeks to yy^. Bichlus 
several months. tracheiphilus 

Numerous well-controlled infection experiments have established 
the causal connection of the bacillus with the symptoms of this 
disease. 

XII. SOFT ROT OF CARROT AND OTHER VEGETABLES 

Bacillns carotovonts Jones 

Harding, H. A., and Stewart, F. C. A Bacterial Soft Rot of Certain Cru-- 

ciferous Plants and Amorphophallus simlense. Science, N. S. 16: 314- 

315. 1902. 
Harrison, F. C. A Bacterial Disease of the Cauliflower {Brassica oleracea) 

and Allied Plants. Ont. Agl. Exp. Sta. Built. 137: \-2?>. figs. 1-18. 1904. 
Jones, L. R. A Soft Rot of Carrot and Other Vegetables. Vermont Agl. Exp. 

Sta. Rept. 13: 299-332. figs. i-io. 1901. 
Potter, M. C. Ueber eine Bakterienkrankheit der Riiben {Brassica Napiis). 

Centrbl. f. Bakt., Parasitenk. u. Infektionskr. 7 (Abt. II): 282-288, 353- 

362. 1901. 
Spieckermaxx, a. Beitrag zur Kenntnis der bakteriellen Wundfaulnis der 

Kulturpflanzen. Landw. Jahrb. 31: 155-178. 1902. 
Van Hall, C. J. J. Bijdragen tot de Kennis der Bakterieelle Plantenziekten : 

176-1S4. 1902. 

Occurrence and effects. This bacillus appears to be one of 
the most common and widespread of the species parasitic upon 
plants. It was not accurately studied until 1901, but has since 
received attention from a number of investigators in different parts 
of Europe and America. It seems safe to say that it is the chief 
producer of that type of disease known as soft rot in vegetables. ^ 

1 Through the kindness of Mr. H. A. Harding, of the New York Agricul- 
tural Experiment Station, I have been able to see the proof of a bulletin by 
H. A. Harding and W. J. Morse on the morphology and cultural characters of 
this organism. This study establishes in a conclusive manner the fact that many 
diseases of vegetables previously referred to other organisms are in reality properly 
caused by this species, and the data here presented are largely based upon the 
study indicated. 



132 



FUNGOUS DISEASES OF PLANTS 




The bacteria invade the intercellular spaces of the host, and 
subsequently the tissues are rapidly disorganized. This disorgani- 
zation is apparently due to an enzyme which attacks particularly 
the middle lamella. A large number of inoculation experiments 
have been made, and it is clearly shown that these bacteria are 
able to produce a form of soft decay in a great variety of plants. 
No other organism yet found has such a wide range of host plants. 
Morphology and cultural characters. The bacillus is in the 
form of short or long rods or chains. According to Jones it 

measures .6 -.09 x i-SSf^, the major- 
ity, however, measuring .8x2^. No en- 
dospores are produced, and it possesses 
from two to ten peritrichiate flagella. 

Upon slanting tubes of agar an abun- 
dant growth is produced. This is fili- 
form to spreading, smooth or contoured, 
and opaque to opalescent in appear- 

FiG. 1,8. Bacillus carotoforus tj. i ii „ i. 4.„ 

, -^ , , r. T o T ^ ance. It also grows well on potato. 
Jones. (After L. R. Jones) » _ ^ 

Gelatin is promptly liquefied, under 
ordinary circumstances, at 20° C. Usually liquefaction begins on 
the second day and is complete in six days ; yet months may be 
required. In bouillon a pellicle is often formed. In other cases 
there is merely a clouding, or finally the development of a floccu- 
lent precipitate. Milk is usually coagulated by the third day, and 
this is so slowly peptonized that the action may not be complete 
for several months. Litmus milk is rendered acid, and the power 
of indol production is possessed to a feeble extent. 

The organism reduces nitrates in nitrate broth to nitrites. The 
thermal death point is about 48 to 50° C. It is also important to 
note that with a majority of the strains gas is produced in small 
amounts with dextrose, lactose, and saccharose. In this gas- 
producing character the forms of the organism from a large 
number of sources show a certain variation, however, which 
reaches an extreme in the form producing soft rot of the calla 
lily, in which case no gas is produced from any of the sugars 
mentioned. The calla lily organism is tentatively retained as a 
distinct species. It represents, at any rate, an extreme form of 
the Bacilhis carotovorns so far as it is at present known. 



schiz()mycp:tes. bacteria 



133 



XIII. SOFT ROT OF THE CALLA 

Bacillus aroidece Townsend 

TOWNSEND, C. O. A Soft Rot of the Calla Lily. U. S. Dcpt. Agl., Bureau 
Plant Industry, Built. 60 : 1-44. ph. i-g. 1904. 

This organism, very closely related to the preceding, has been 
found to be the cause of a serious soft rot of the calla lily, 
destroying the plants at about the time of flowering. The seat 




Fig. 39. IsoL.'^TioN Culture of Bacillus aroidr.-f. Townsend. 
(Photograph by C. O. Townsend) 

of the disease is principally in the corms, petioles, and flower 
stalks. If inoculated into a wound, the bacillus will produce a 
rot in many raw vegetables, and also in some green fruits. The 
cultural characters have been indicated. According to Town- 
send it produces on agar very characteristic radiate colonies 
(Figs. 38, 39) at or near the optimum temperature. The rot 
in the calla may be prevented by a careful selection of the corms 
and by changing the soil in the beds every three or four years. 



134 



FUNGOUS DISEASES OF PLANTS 



XIV. WILT OF SOLANACE^ 
Bacillus solanacearum Erw. Smith 

Smith, Erw. F. A Bacterial Disease of the Tomato, Egg Plant and Irish 
Potato. U. S. Dept. Agl., Uiv. Veg. Phys. and Path. Built. 12: 1-26. 
pis. 1-2. 1896. 

Smith, Erw. F. The Granville Tobacco Wilt. U. S. Dept. Agl, Bureau 
Plant Industry, Built. 141 (Pt. II): 17-24. 1908. 

This is a germ which, in the United States, causes an important 
wilt and drying up of potatoes, tomatoes, and eggplants. In the 

far South it is particularly destruc- 
tive to tomatoes. It has also been 
found in Europe and Asia. When 
potato vines are affected there is a 
blackening of the fibrovascular sys- 
tem of the tuber, and eventually a 
black rot may set in. The organism 
is aerobic and an alkaline reaction 
is produced. No gas is evolved, 
and gelatin is not, or only very 
slightly, liquefied. Recently it has 
been found that this organism pro- 
duces also the Granville tobacco wilt. 



i 



W 



Fig. 40. SuiicuLTURE ok B.ic/llus 
AROWE^ ON Agar Slant. (Photo- 
graph by C. O. Townsend) 



XV. BACILLUS: OTHER SPECIES 

Among other disease-producing organisms of this genus may 
be mentioned the following : 

Bacillus HyaciiitJn-scpticns Heinz, ^ causing rapid death of cul- 
tivated hyacinths. 

Bacillus Cubonianus Macch.,^ said to be the cause of an 
important leaf and twig disease of the mulberry, especially in 
France and Italy. 

1 Heinz, A. Zur Kenntniss der Rotzkrankheiten der Pflanzen. Centrbl. f. 
Bakt. u. Parasitenk. 5 : 535-539. 18S9. 

2 Macchiati, L. Sulla biologia del Bacillus Cubonianus, sp. nov. Malpighia 5 : 
289-301. //. 21. 1 89 1. 



CHAPTER X 

PHYCOMYCETES 

The Phycomycetes are commonly called the algal-like fungi. 
They are very diverse both with reference to the characteristics 
of the vegetative and of the reproductive stages. The habits of 
these forms, moreover, are so varied that a discussion of such 
peculiarities may be postponed until the individual families are 
described. The lower forms show very little differentiation or 
complexity of vegetative parts, and the fungous body may indeed 
consist of a single simple cell. In other forms the fungous body 
possesses short branches or thread-like parts, which may be desig- 
nated JiypJuc. In the higher forms there is a well-developed my-, 
celium, or system of branching hyphse. These vegetative hyphas 
are commonly siphonaceous (nonseptate), but sometimes cross 
walls (septa) are produced. In fact, there are families in which 
the mycelium is constantly siphonaceous until the reproductive 
cells are cut off, and cross walls occur only in conjunction with 
spore development. In other cases the hyphae are siphonaceous 
when young, becoming generally septate with age. 

The methods of reproduction are either by means of nonsexual 
or sexual spores. The nonsexual spores are produced either within 
differentiated portions, usually tips of branches, in which case these 
differentiated parts are termed sporangia ; or the spores (conidia) 
may be produced upon hyphse, in which case the latter are known 
as conidiophores. In some genera the conidia also become spo- 
rangia germinating by the production of motile spores, zoospores. 
Sexual reproduction by the union of differentiated cells (gametes) 
is common in the higher forms only, and the gametes may be 
equal or unequal in size. The higher forms, however, constitute 
the majority of these fungi. 

The Phycomycetes contain seven orders. Two of these, Ancy- 
listales and Monoblepharidales, are small groups of water fungi. 
One order, the Mucorales, is an unusually interesting group, 

135 



136 FUNGOUS DISEASES OF PLANTS 

composed, however, largely of saprophytic organisms, and a fourth 
order, Entomophthorales, contains forms which are for the most 
part parasitic upon insects. There remain therefore three orders 
which are important from the standpoint of diseases in plants, viz., 
Chytridiales, Saprolegniales, and Peronosporales. 

I. CHYTRIDIALES 

Farlow, W. G. The Synchytria of the United States. Bot. Gaz. 10: 235- 

245. pi. 4. 1885. 
Harper, R. A. Cell-Division in Sporangia and Asci. Ann. Bot. 13 : 467- 

525. pis. 24-26. 
KusANO, S. On the Cytology of Synchytrium. Centrbl. f. Bakt., Paras, u. 

Inf. 19 (Abt. II): 538-543. pi. i. 1907. 
NowAKOWSKI, L. Beitrag z. Kenntnis d. Chytridiaceen. Cohn's Beitrage z. 

Biol. d. Pflanzen 2: 73-100, 201 -2 19. pis. 4-6, S-g. 1876. 
RvTZ, Walter. Beitrage zur Kenntnis der Gattung Synchytrium. Centrbl. 

f. Bakt., Paras, u. Inf. 18 (Abt. II): 635-655, 799-S25. 1907. 
SCHROETER, J. Die Pflanzenparasiten aus der Gattung Synchytrium. Bei- 
trage z. Biol. d. Pflanzen. 1 : 1-132. pis. i-j. 1870. 
SCHROETER, J. Chytridinese. Pflanzenfamilien (Engler and Prantl) 1 (i* 

Abt.): 6^-%j. Jigs. 4g-yi. 1892. 
ZoPF, W. Ueber einige niedere Algenpilze. 1887. Halle. 

In a consideration which might include several hundred fungi 
of greatest economic importance, as disease-producing organisms 
of the flowering plants, doubtless no mention would be made of 
the above order. The order should, however, receive at least casual 
attention at the hands of the student, owing to the important posi- 
tion which it occupies as the lowest of the true fungi. It is a strik- 
ing fact that a considerable majority of these lower fungi are parasitic 
upon protozoa, algae, and other fungi. Some, however, are para- 
sitic upon higher plants. 

These plants are all very simple, and there is no member of 
the family which possesses a true mycelium, although delicate 
branches of the fungous body occur. Reproduction is accom- 
plished by means of motile spores, or swarm cells, produced in 
sporangia. In higher forms cell fusions occur. It is not certain 
what these fusions denote. 

II. SYNCH YTRIACE^ 

In this family are included the majority of the Chytridiales 
parasitic upon higher plants. They occur for the most part only 



PHYCOMYCETES 



^?>1 



upon plants growing in moist situations. A motile spore, zoo- 
spore, comes to rest upon an epidermal cell, and penetration 
doubtless results after a minute perforation is made, by the 
streaming through of the protoplasmic body. There are no evi- 
dences of a mycelium. The presence of the parasite in the 
epidermal cell may in time cause a minute gall-like abnormality 
of the host. The small galls are sometimes so numerous as to 
give the host the appearance of being affected by a rust fungus. 





Fig. 41. Synchytrium on Pueraria, Stages in the For- 
mation OF THE PoLYNUCLEATE FuNGOUS BoDY AND THE 

Lysigenous Cavity. (After Kusano) 

The simple protoplasmic mass resulting from the growth of the 
penetrating swarm spore becomes either a fruit body, sorus, or 
a resting spore ; in the latter case it becomes a fruit body ulti- 
mately, and this, at maturity, breaks up into numerous sporangia, 
and may therefore be termed a sorus, each sporangium eventually 
producing swarm cells. 

Harper has studied from a cytological point of view the de- 
velopment of Synchytriinn decipiens Farl., and from this study 
may be distinguished seven more or less distinct stages in the 
life cycle of this organism: (i) after the swarm spore comes to 



138 FUNGOUS DISEASES OF PLANTS 

rest and penetrates the epidermal cell of the host there is con- 
siderable growth in this single cell of the fungous, vegetative 
body ; (2) multiplication of the nuclei in the vegetative body until 
a considerable number is formed ; (3) progressive cleavage in the 
multinucleate body from the surface inward, such that uninu- 
cleate bodies (termed protospores) are produced, accompanied 
with marked shrinkage of the segments ; (4) growth, increase 
in size of the protospores, followed by nuclear divisions ; (5) the 
development of cell walls about the multinucleate spores, food 
storage, and passage into a ripened or resting condition ; (6) 
germination by the production of a sporangium from each multi- 
nucleate spore, each sporangium producing a number — usually 
eight to twelve — of the uninucleate, uniciliate spores ; (7) the 
active motile stage. 

In a recent study Kusano reports that a Synchytrium on Pueraria, 
and also Syiichytrinvi dccipicns, affect only nonchlorophyllous cells 
of the mesophyll. In each he finds that the cell wall of the affected 
cell (and in time of neighboring cells) is dissolved. Eventually con- 
siderable lysigenic cavities are formed in which the fungous body 
lies "encased by the symplast of the host" (Fig. 41). 

Synchytrium. In this genus the fruit body, upon reaching 
maturity, forms no highly resistant cell wall about itself, but by 
immediate differentiation of the protoplasmic contents becomes 
the sporangial sorus. 

Pycnochytrium. The fruit body is a thick-walled resting spore, 
which after a period of inactivity germinates by the protrusion of 
its contents in the form of a thin-walled sporangial sorus. The 
sporangia produce uniciliate swarm spores. 

III. CRANBERRY GALL 
Synchytrium Vacdnii Thomas 

Halsted, B. D. Some Fungous Diseases of the Cranberry. N. J. Exp. 

Sta. Built. 64: 1-40. Jigs. j-j8. 1889. 
Shear, C. L. Cranberry Diseases. Bureau Plant Industry, U. S. Dept. Agl. 

Built. 110: 1-64. pis. /-/. 1907. 

It attacks young stems and leaves as well as flowers and fruit. 
The small galls, reddish in color, are produced on the surfaces of 
the parts affected in great numbers. The fungous body consists 




PHYCOMYCETES 1 39 

of a cell (Fig. 42), which becomes a spore, or properly a spo- 
rangium, producing upon germination a mass of swarm spores. 
These spores, being dependent upon 
abundant moisture for their distribu- 
tion, may be rendered more or less 
ineffective by withholding water from ^ 

the cranberry plants during the winter. ''^njPlU'O'^^S v- 
This fungus also occurs upon other 
ericaceous plants more or less closely fig. 42. Cranberry Gall: 
related to the cultivated cranberry. Resting Spore Stage 

IV. PYCNOCHYTRIUM GLOBOSUM (Schroet.) Schroet. 

This is a parasite common in Europe and America on many 
families of flowering plants. In the United States it has been 
found on plants growing in the peat bogs of the eastern states, 
some of the hosts observed being a species of violet, wild straw- 
berry, blackberry, and maple seedlings. It causes the development 
of small but noticeable yellow or reddish galls. 

The entrance of the swarm spore into an epidermal cell is, as 
indicated above, followed by general growth of the protoplasmic 
mass. The affected epidermal cell may become somewhat in- 
vaginated, but the enlargement due to the growth of the fungous 
cell within is such as to give the appearance of a minute gall. 
The resting spore is shown in Fig. 42 as it appears in mid- 
summer. Later there results, as indicated, the sporangial sorus, 
each sporangium of which, upon germination, produces the char- 
acteristic uniciliated swarm spores. 

V. CHYTRIDIALES: OTHER SPECIES 

Among other Synchytriacese more or less commonly found in 
the United States are SyncJiytriimi decipicns Farl. on the hog 
peanut, Amphicarpa nionoica ; Synchytrhim fulgens Schroet. on 
the evening primrose, CEnothera biennis ; Pycnochytriuni anreinn 
(Schroet.) Schroet. occurring upon numerous hosts ; and Pycno- 
chytrijim Myosotidis (Kiihn) Schroet, on certain Boraginaceae and 
Rosaceae. In a different family, Oochytriacese, may be included 
some interesting parasites of economic plants. These fungi 



I40 FUNGOUS DISEASES OF PLANTS 

are certain members of the genus Urophlyctis,^- ^ Urophlyctis 
lepivides (Trabut) Magn. occurs on root outgrowths of the beet, 
Beta vidgaris ; Urophlyctis p7dposa (Wall.) Schroet. attacks 
leaves and stems of species of Chenopodium and Atriplex ; 
and Urophlyctis Alfalfce (v. Lagerh.) Magn. is found upon the 
roots of alfalfa, Medicago sativa, in South America and in 
Germany. 

VI. SAPROLEGNIALES 

The Saprolegniales are commonly called water molds on 
account of the fact that the majority of these fungi occur in 
the water, usually in ponds and streams, upon dead insects and 
other small animals, or sometimes upon other organic matter. 
One or more species attack fish, producing important diseases. 
A few members of the order, however, are not properly water 
molds, being found upon plants in moist places, some parasitic 
and some saprophytic. In the aquatic forms there is a con- 
siderably branched mycelium, habitually without septa, except 
where spore-producing parts are cut off. The hyphae are fre- 
quently of large diameter and readily evident to the unaided 
eye. Nonsexual spores are produced in terminal sporangia. 
Upon liberation the spores usually become motile. Sexual repro- 
duction is by means of unequal gametes, produced in oogonia 
and antheridia. The latter are sometimes wanting ; moreover, 
when present there are cases (certain aquatic forms) where they 
are apparently functionless. 

Pythiaceae. The Pythiaceae include such members of the 
Saprolegniales as are important in plant pathological study. 
The family has some characters which seem to indicate that 
they might with equal propriety be placed in the order next 
discussed, Peronosporales. The species which are of interest 
in this connection are those which cause damping-off, rot, or 
somewhat similar diseases in seedlings, or in delicate plants. 
This family differs from the remaining coordinate members of 
the order in the complete differentiation of the sporangia from 

^ Magnus, P. Ueber eine neiie unterirdisch lebende Art der Gattung Uro- 
phlyctis. Ber. d. deut. hot. Ges. 19 : 145-150. //. sy. 1901. 

2 Magnus, P. Ueber die in den knolligen Wurzelauswuchsen der Luzerne 
lebende Urophlyctis. Ber. d. deut. bot. Ges. 20: 291-296. //. 75. 1902. 



PHYCOMYCETES 141 

the general vegetative hyphae, and also in the production of 
other nonsexual spores, conidia, borne upon hyphae, which 
spores germinate by means of a germ tube, and not by the pro- 
duction of motile spores. The antheridia are always functional, 
and the process of fertilization is apparently exactly the same as 
in the majority of the Peronosporales. Pythium and Pythiacystis 
are important genera. 

VII. A DAMPING-OFF FUNGUS 
Pythium dc BaryaniiDi Hesse 

Atkinson, Geo. F. The Potting Bed Fungus. Cornell Univ. Agl. Exp. Sta. 

Built. 94: 234-247. pi. I. 1894. 
Hesse. Pythium de Baryanum, ein Endophytischer Schmarotzer. 1874. Halle. 
MiYAKE, K. The Fertilization of Pythium de Baryanum. Ann. Bot. 15 : 

653-667. pi. 36. 1 90 1. 
Ward, H. Marshall. Observations on the Genus Pythium (Pringsh.). 

Quart. Journ. Mic. Sci. 23: 485-519. ph. 34-36. 18S3. 

Habitat relations. This species is, perhaps, from an economic 
point of view, the most important in the order. It is very com- 
mon in greenhouse and garden soil both in Europe and America, 
and it is a cause of one of the various greenhouse maladies known 
as damping-off in seedlings. The conditions which favor the de- 
velopment of the fungus are a considerable degree of warmth, 
abundant moisture, and weakened condition of the seedlings. It 
is especially common when the plants are being grown in a very 
crowded condition. While most common in the greenhouse, it 
may affect the crop in the field as well. This fungus infests a 
variety of seedlings, but those of the cress, cucumber, sunflower, 
and others are particularly susceptible. White clover, several cru- 
cifers, corn and other members of the grass family are likewise 
included among the hosts. 

Symptoms. The effects of this fungus may be evident upon 
the seedlings a few days after germination. The point of attack 
is ordinarily at or near the surface of the ground. The tissues 
of the affected region promptly lose their turgidity and usually 
appear water soaked (Fig. 43). When the tissues collapse the 
seedlings fall prostrate, and then the mycelium invades the re- 
mainder of the plant, if the latter is kept moist by contact with 
the damp soil. 



142 



FUNGOUS DISEASES OF PLANTS 




Fig. 43. Bean Seedlings attacked by Pythium 
(Photograph by H. H. Whetzel) 

The fungus. The mycelium, like that of most Peronosporaceae, 
is delicate, more or less variable in diameter, and much branched. 
The branches are, for a time, at least, smaller than the parent 
hyphas. The protoplasm is densely granular in the growing 



PHYCOMYCETES 



14: 



portions. The hyphae are apparently intercellular at first and after- 
wards intracellular. 

Terminal or intercalary spherical sporangia are sparingly pro- 
duced. These are usually persistent, and may be from three to 
five times the diameter of the hyphae. During germination a 
short tube is developed at one side, and through this the my- 
celium migrates, forming a kind of swarm sphere within which it 
breaks up into bean-shaped masses, which are set free as zoospores 
with two lateral (Hesse figures only one) cilia. Thicker walled 
sporangia-like bodies, called conidia, are also produced. These 
are deciduous, and germinate immediately by forming zoospores. 




Fig. 44. Mycelium of Pythium invading Tissues 

Thick-walled resting conidia also appear, and these eventually 
germinate by means of a germ tube. 

The oogonia, or egg-bearing gametes, are formed either as 
terminal or intercalary enlargements, and are of much the same 
form as the sporangia. When two or three times the size of 
a hypha they are cut off from the vegetative cells. The proto- 
plasm is gradually differentiated into a central denser portion, 
ooplasm, or oosphere, and a less dense peripheral " periplasm." 
A coincident development of an antheridium or male gamete 
takes place, the latter arising either as the enlarged terminal 
portion of a separate antheridial branch (from the same or from 
a different hypha), or as a lateral cell cut off directly adjacent 
to the oogonium. More than one antheridium may be present, 
each coming in contact with the oogonium. From an anther- 
idium a fertilization tube grows into the oosphere, and through 
this tube a nucleus and some cytoplasm pass in, and the nucleus 
fuses with the nucleus of the oosphere (Fig. 45). This process 



144 



FUNGOUS DISEASES OF PLANTS 



has been carefully studied, and the evidence must be accepted. 
Subsequently, a thick wall forms about the oosphere, which now 
properly becomes the mature egg, or oospore, 
measuring ordinarily 2 5 -3 5 /a in diameter. 
The development of an oospore may be com- 
pleted, under favor- 
able conditions, in 
a single day. 

Since this fungus 
may readily con- 
tinue its growth 
into dead tissues it 
may be cultivated 
indefinitely in Van 
Tieghem cells or in 
specially devised cul- 
ture chambers, and 
the various repro- 
ductive processes 
may therefore be carefully followed. It is evident that with care 
the fungus might be isolated and grown in pure cultures. The 
material of the genus Pythium from various hosts and localities 
should be carefully studied and compared under control conditions, 
as there is much doubt concerning the validity of species. 




V\r,. 45. Sexual Repkoductio, 
{a, after Miyake) 



IN Pythium 



VIII. BROWN ROT OF THE LEMON 
Pythiacystis Citrophthora R. E. Smith 

Smith, R. E. A New Fungus of Economic Importance. Bot. Gaz. 42: 215- 

221. Jigs. I -J. 1906. 
Smith, R. E. The Brown Rot of the Lemon. Cahf. Agl. Exp. Sta. Built. 

190: 1-70. Jigs. i-2g. 1907. 

Occurrence. The brown rot of the lemon is a disease which 
has become very prominent in the region of lemon production 
in California during the past few years. It affects more or less 
every operation having to do with lemon production and market- 
ing, and at the time of the investigations which were undertaken 
in California for its control it seemed to threaten the stability 
of this industry. The brown rot may be found in the orchard, 




PHYCOMYCETES 1 45 

in the packing house, and in storage conditions. From the 
description subsequently given it may be readily distinguished 
from forms of decay due to common mold fungi. It is most 
serious in connection with lemon growing, but the fungus pro- 
ducing the disease may also affect to a slight extent at least the 
orange, pomelo, and other citrous fruits. In the orchard the dis- 
ease may be found upon fruit which has fallen, or that which 
is hanging very close to the moist soil. It is most abundant 
during wet weather, or follow- 
ing irrigation, and is therefore 
intensified where the soils are 
heavy. It is estimated that under 
favorable conditions for the fun- 
gus a box of lemons per tree 
is no extraordinary loss. 

Symptoms. The first indica- 
tions of the trouble may be noted 
in a brownish or purplish dis- Fig. 46. Bkuwin Rot ok Lemon 
coloration of the rind, showing '^^^^^^ ^- ^- ^^^^^^ 

light on the greener fruit, and darker on the yellow fruit. Both 
young and old, vigorous and weak fruits alike are affected, and 
the disease is particularly characterized by a marked and peculiar 
odor, by its rapid spread from fruit to fruit, in the packing house, 
or while stored in boxes, and by the presence of small flies 
wherever the affected fruit is stored in quantity. After storage 
for a week or ten days there may develop upon the affected 
lemons a white mold-like growth (Fig. 46), and frequently upon 
such affected fruit there is subsequently produced also the blue 
mold, Penicillium. The blue mold alone, however, does not 
spread rapidly, and has not the peculiar odor of the brown- 
rot disease. The disease may appear upon fruit in storage, 
which seemed to be perfectly colored and sound when passed 
by the washer. 

The fungus. The fungus concerned in the production of this 
decay is apparently one which was unknown until attention was 
directed to this lemon disease, and which, while it is an active 
parasite of citrous fruits, it is doubtless ordinarily a common sapro- 
phyte found in moist soils and in water. The mycelium of this 




146 FUNGOUS DISEASES OF PLANTS 

fungus penetrates the rind and other fibrous portions of the 
lemon to a considerable extent ; it is much branched, irregular 
in diameter, and extensive. Upon the lemon, as a rule, no form 
of spore is produced, but there is developed frequently a con- 
spicuous aerial growth due to the emergence 
of many mycelial branches. In some cases 
these are produced in more or less tuber- 
culate masses. Conidia and sporangia appear 
under favorable conditions. In moist soil near 
affected fruit the sporangia are developed 
abundantly upon a fine much-branched my- 
celium (Fig. 47). The sporangia measure 
20—60x30—90/1. (averaging 35x50^1). 
They are lemon-shaped, or subspherical with 
pronounced apical protuberance. In water 
Fig. 47. Sporangia of germination is effected by means of a vari- 
Pythiacystis.^^^ (After ^|^j^^ number of zoospores, often about thirty, 
each biciliate with long cilia (Fig. 48). 
Control. Ordinarily the fungus does not produce any spore 
stage upon the surface of the lemon. On moist soil, however, 
it produces sporangia and sometimes conidia. 
The infection of the fruit usually takes place v. ^ C 
in the orchards, and also subsequently by yO 
direct contact and also by the operation of 
washing. It has been found, for instance, 
that if uninfected lemons are dipped in water 
in which diseased ones have been washed, 
infection will in time result on the healthy 
fruit. In fact, the ordinary wash water may 
itself contain a large number of germs of 
this fungus and it may also live more or less fig. 48. Germinating 
permanently in the machine used for wash- Sporangium of Pythia- 
ing such fruit. The remedy, therefore, for c^s-ns. (After R.E.Smith) 
such conditions is very simple and merely consists in treating 
the water used for washing purposes with some aseptic or toxic 
agent. The most practicable method which has been devised con- 
sists in using copper sulfate, formalin, or potassium permanganate. 
In using formalin one part of the reagent to ten thousand parts 




PHYCOMYCETES 1 47 

of water may be employed, or i pint to 1250 gallons has been 
sufficient to check the infection. Permanganate of potash is rather 
a mild disinfectant as compared with formalin and it is necessary 
to use I pound to 625 gallons. A stronger concentration dis- 
colors slightly and the former strength is advised. Copper sulfate, 
which is both a cheap and effective disinfectant, may be used, 
of about the same strength as the permanganate of potash. Care 
should be taken that this is not employed in a very much more 
concentrated form, i pound to 250 gallons, for instance, resulting in 
injury in the form of a burn. Unfortunately, however, this substance 
attacks the arm of the tank and is therefore less desirable than 
those previously referred to. A higher concentration of blue stone 
is needed on account of the alkalinity of the water used. In dis- 
tilled water, one part of blue stone to one million will be effective. 

IX. PERONOSPORALES 

De Bary, a. Zur Kenntnis der Peronosporeen. Bot. Zeit. 39: 521-530, 537- 

544, 553-563, 569-578, 585-595, 601-609, 617-625. pi. 3. 1881. 
Farlow, W. G. Enumeration of the Peronosporeae of the United States. 

Bot. Gaz. 8: 305-315. 327-337- 1883- 
LiJSTNER, G. Untersuchungen iiber die Peronospora-Epidemien der Jahre 

1905 und 1906. Ber. d. Konigl. Lehranstalt fiir Wein-, Obst- und Gar- 

tenbau, Geiscnheim a/Rh. (1906): 1 19-140. 
ROSTOWZEW, S. J. Beitrage zur Kenntnis der Peronosporeen. Flora 92 : 

405-430. pi. II -I 3. 1903. 
SCHROETER, J. Peronosporinese. PflanzenfamiUen (Engler u. Prantl) 1 (i* 

Abt.): \o'^-\\(). figs. g2-i02. 1893. 
Swingle, W. T. Some Peronosporaceae in the Herbarium of the Division of 

Vegetable Pathology. Journ. Mycol. 7 : 109-130. 1892. 
Wilson, G. W. Studies in North American Peronosporales. I. The Genus 

Albugo. Torrey Bot. Club Built. 34: 61-84. 1907. II. Phytophthoreas 

and Rhysotheceas. Ibid. : 387-416. 

The members of this order are entirely parasitic, many of 
the species causing important diseases of cultivated plants. The 
mycelium is well developed, siphonaceous, and, with exceptions 
in one genus (Phytophthora), intercellular. The asexual spores, 
which may in general be termed conidia, are produced upon 
erect conidiophores, which are from the first, or which ultimately 
become, aerial. The conidiophores may be simple or diversely 
branched. The conidia germinate either by means of a germ 
tube or by the production of motile spores, zoospores ; in the 



148 FUNGOUS DISEASES OF PLANTS 

latter case the conidium becomes a zoosporangium. Oogonia 
and antheridia are also present, and these are produced within 
the tissues of the host. The oospores upon germination give 
rise to numerous zoospores or to a single germ tube. Some 
members of both families (Albuginaceae and Peronosporacese) of 
this order deserve careful study. To the genus Phytophthora of 
the Peronosporaceae Pythium and Pythiacystis are perhaps closely 
related. 

Albuginaceae. In this family the conidia are borne in chains ; 
the conidiophores arise in the form of large cushions which 
might be termed sori. They are developed beneath the epi- 
dermis, but the latter is finally ruptured, and the conidia are 
exposed. The oospore germinates by the production of zoo- 
spores. There is one genus, Cystopus. 

Peronosporaceae. The members of this family are distinguished 
from the preceding largely by the conidiophores, which are from 
the beginning aerial. The conidia are also produced singly. This 
is properly the family of the downy mildeivs. The mycelium, 
which is commonly intercellular, develops either branched or 
knob-like haustoria. The oospore germinates by means of a 
germ tube. 

The following generic key includes most of the genera together 
with the salient generic characteristics, and is, in this family, more 
practical than a description of each genus : 

A. Conidiophore fully developed prior to the formation of conidia. 

1. Conidium on germination becoming a swarm sporangium (zoo- 

sporangium). Oospore free from the wall of the oogoniuni. 
Plasmopara 

2. Conidium becoming a swarm sporangium, conidiophore short, 

irregular in form and diameter, oospore filling oogonium, with 
closely adherent walls Sclerospora 

3. Conidium germinating by means of a germ tube. 

a. Conidium provided with a terminal papilla from which 

the germ tube proceeds. Fertile tips arising from a 
disk-like swelling Bremia 

b. Conidium without papilla. Fertile tips ordinarily branch- 

like Peronospora 

B. Conidiophore incomplete when first conidia produced. Fertile tips 

swelling and continuing growth as successive conidia are formed. 
Phytophthora 



PHYCOMYCETES 1 49 

X. WHITE "RUST" OF CRUCIFERS 
Cystopiis candidus (Pers.) Lev. 

Davis, B. M. The Fertilization of Albugo Candida. Bot. Gaz. 29: 296-310. 

pi. 22. 1900. 
Wager, H. On the Structure and Reproduction of Cystopus candidus Lev. 

Ann. Bot. 10: 295-339. ph. ^j, 26. 1895. 
Zalewski, a. Zur Kenntniss der Gattung Cystopus Lev. Bot. Centrbl. 15 : 

215-224. 1883. 




Fig. 49. Flowers and Peduncles of Radish deformed by Cystopus 
(Photograph by H. H. Whetzel) 

The common white "rust" of cruciferous plants appears to 
be common throughout the world. The fungus is frequently 
one of the first of the order to make its appearance in the spring 
and the last to disappear in winter. Evidently, it is not readily 
affected by minor climatic differences, and probably slight dews 
are sufficient to insure its propagation. 

This fungus is most common upon the forms of the ubiqui- 
tous shepherd's purse {Capsella Bitrsa-pastoris) ; but it is also 
common upon the radish {Raphamis sativus), horse radish 
{Cochlearia Armoracia), cress {Brassica oleracea), turnip {Bras- 
sica Rapa), mustard [Brassica nigra), water cress {Radicnla Nas- 
tiirtiimi-aquaticwn) , etc. 



I50 



FUNGOUS DISEASES OF PLANTS 



The effects of the fungus are somewhat various 



Symptoms 

upon the different hosts. Upon the shepherd's purse the stems 
are enlarged and distorted, while no unusual malformations of 
floral organs and leaves generally occur. On the radish the floral 
organs may be strikingly hypertrophied (Fig. 49), ovary sacs 
greatly enlarged, stamens, petals, and sepals distended and some- 
times becoming leaf-like. Upon nearly all hosts the porcelaneous 




Fig. 50. CoNiDiAL Stage, Fertilization, and Germinating 
Oogonium of Cystopus. (/^ and c, after Ue Bary) 



conidial cushions, characteristic of the family to which this species 
belongs, are prominent. 

The fungus. The conidial cushions occur upon leaves, stems, 
and floral parts, or fruits. On the majority of hosts, such as 
shepherd's purse, horse radish, etc., oospores generally occur only 
in the stems, yet upon some other hosts, particularly upon certain 
mustards in the western United States, oospores alone are com- 
mon. The mycelium is considerable, and constantly intercellular, 
with abundant knob-like haustoria. The mycelium develops abun- 
dantly at some points just beneath the epidermis, and there are 
produced numerous short, erect, basally branched conidiophores. 
The latter give rise to simple chains of spores in basipetal suc- 
cession. These are usually separated one from another by slight 



PHYCOMYCETES 



151 




beak-like projections. The developing cushions break the epidermis 
and the mature spores are set free. Fig. 50,^7, shows a section 
through a conidial cushion. Under favorable conditions germina- 
tion of the conidia proceeds promptly and each conidium becomes 
a zoosporangium, the protoplasmic contents dividing into six or 
more parts which emerge through 
an opening developed either ba- 
sally or terminally. The zoospores 
are set free as ovate swarm cells 
with two unequal lateral cilia. 
After a brief motile period they 
come to rest, become invested 
with a cell wall, and may push 
out a germ tube in a few hours. 

The oospores are normally 
produced later than the conidia. 
The oogonia and antheridia de- 
velop in the intercellular spaces, 
and the mode of formation is Fig. 51. Fertilizatiun in Cystopus 
much as in Pythium. The oogonia ^^^'^' ^- ^- ^^^'^^ 

are, however, in this case larger, measuring from 50 to 60 /x in 
diameter. There are numerous nuclei in the early stages. It is 
generally agreed that in this species the differentiation of the 
ooplasm is accompanied by a migration of the nuclei to a pe- 
ripheral position and the organization of a central body termed 
a coenocentrum. A nucleus then returns from this nuclear zone 
to the region of the coenocentrum. Preceding the latter, however, 
it is held that one karyokinetic division may be constantly found. 
The zone of the now disintegrating nuclei indicates fairly well the 
line of differentiation between periplasm and ooplasm. As the 
antheridial tube penetrates, a cell wall begins to be laid down be- 
tween ooplasm and periplasm. Into the tube of the antheridium 
a single antheridial nucleus migrates. 

Special attention is called to the fact that at maturity of the 
egg there is a single nucleus in each gamete, but the egg is also 
provided with a coenocentrum. Fertilization proceeds exactly as 
in Pythium, and during the nuclear fusion the coenocentrum 
promptly disappears. Fig. 5 1 shows the oosphere with developing 



152 FUNGOUS DISEASES OF PLANTS 

wall, the remains of the antheridium, the fusion nuclei, and 
the coenocentrum. The wall of the mature oospore is brown in 
color and sculptured in a characteristic manner. The oospores 
are 35-40/i in diameter. It is believed that nuclear division 
proceeds, during the maturity of the oospores, until about thirty- 
two nuclei are present, and it has been suggested that each of 
these divides twice preceding germination, which again takes 
place by the formation of zoospores. A period of rest is invari- 
ably required between maturity and germination. 

XI. CYSTOPUS: OTHER SPECIES 

Other species of Cystopus which are very generally distributed, 
occurring on common hosts of the garden and field, are 

Cystopus Tragopogonis Pers,, found on salsify {Tragopogon por- 
rifolius) and various other Compositae ; 

Cystopus convolvulacearum Otth., on species of the morning 
glory and sweet potato family, Convolvulaceae ; 

Cystopus Bliti (Biv.) Lev., on several species of pigweed, Ama- 
rantaceae. The oospores of this species are often very abundant 
in late autumn ; the stems and flower spikes in which they occur 
are deformed and usually purplish. 

XII. DOWNY MILDEW OF THE GRAPE 
Plasmopara Viticola (B. & C.) Berl. & De Toni 

CoRNU, M. Etudes sur les Pdronospor^es. [Observations sur le Phylloxera 

et sur les parasitaires de la vigne.] 1: 101-184. 18S1 ; 2: 1-91. 1882. 
Farlow, W. G. On the American Grape-Vine Mildew. Built, of the Bussey 

Institution (1876): 415-425. pis. 2-j. 
Report on Experiments made in 1888 in the Treatment of the Downy Mildew 

and Black Rot of the Grape Vine. Bot. Div., U. S. Dept. Agl. Built. 10: 

1-61. 1889. 
ScRiBNER, F. L. The Fungous Diseases of the Grape Vine: I. The Downy 

Mildew. Bot. Div., U. S. Dept. Agl. Built. 2 : 7-18. pis. /, 2, 4 (in part). 

1886. 
VlALA, P. Mildiou. Les maladies de la vigne (Chap. 2): 57-155- t^^- 2-3. 

Jigs. 20-46. 1893. Montpellier et Paris. 

Occurrence. The downy mildew of the grape is one of the 
most important disease-producing organisms among the Pero- 
nosporaceae. The fungus seems to be of American origin, and 



PHYCOMYCETES 



153 



was at first probably more or less confined to the Mississippi 
Valley and states to the eastward. It has been known for a 
long time as a pest in the Middle Atlantic States, extending 
westward to the Mississippi, but in the states farther to the 




Fig. 52. Grape Leaf with Early Stage of Downy Mildew 
(Photograph by H. H. Whetzel) 

northeast, while equally common, it has been less disastrous in 
its effects. This is to be accounted for in part by the vigorous 
growth of the vine under more constant rainfall ; but the greater 
injury farther west has been attributed particularly to the fact 
that the fungus appears earlier in the season. The disease was 



154 FUNGOUS DISEASES OF PLANTS 

not known on the Pacific Slope during the early history of 
grape-growing in that region, but it is now not uncommon. The 
fungus was apparently introduced into Europe from America, 
and it became a serious pest within a very short time after it was 
first noted in that country. This greater injury under European 
conditions had been predicted by Farlow on account of the early 
spring and the relatively slight growth which is made by Vifis 
vinifera, the cultivated grape of Europe. 

The grape mildew has been found abundantly on practically all 
species of cultivated or wild grapes, that is, upon such species as 
Vitis (sstivalis, J Itis cordifolia, Vitis Labmsca, and Vitis vmifera. 
It occurs, therefore, on the smooth-leaved species as well as on 
those possessing a downy lower surface, and there are few varie- 
ties which are notably resistant under all conditions. 

This fungus attacks practically all young or green portions 
of the growing vine, — leaves, shoots, and berries. The vine may, 
therefore, under conditions favorable for the development of the 
fungus, show the disease abundantly. Under ordinary condi- 
tions, however, it is largely confined to the leaves, and its in- 
jurious action consists in the production of discolored spots which 
prevent or inhibit normal physiological activities (Fig. 52). A 
slight attack of this fungus may, however, cause no perceptible 
diminution of the amount of the grape crop. Under ordinary 
circumstances the fungus may be found in the early summer, 
particularly if the season is moist, and it may reach its greatest 
intensity during August or as late as September. 

Symptoms. Upon the leaves the first indications of the disease 
are indefinite spots, which from the upper surface are yellowish 
in color and irregular in size and form. Upon the lower surface 
of the leaf the spots are not so evident, but almost simultaneously 
with the spots above, the sporophores of the fungus are produced 
on the lower surface. Later in the season the spots may turn 
brownish above, and upon some varieties of grapes they may 
be almost brown from the beginning, finally appearing as small, 
angular brown spots, visible on both surfaces of the leaf. It is 
only when the fungus is very severe that the leaf dries and falls 
prematurely. Upon the shoots depressed areas, dark in color, are 
produced, and these therefore bear no resemblance to anthracnose, 



PHYCOMYCETES 



155 



which may appear upon the shoots, as subsequently described. 
Commonly the fungus is found upon the berries only when the 
latter are young, although a form of brown rot, sometimes called 
gray rot, may be produced by this fungus when the berry is more 







Fig. 53. Plasmopara on Grape, (b and d after Farlow) 

<7, mycelium ; b, mature conidiophore ; c and d, zoospore and oospore 

formation, respectively 

than two-thirds grown (see illustration facing page i). Upon Vitis 
cordifolia the fungus may fruit so abundandy upon the young berries 
as to completely envelop them in a downy mass of sporophores. 
Under such circumstances the berry does not at that stage show 
evidences of decay, and it is only when the berries are older, and 
in other species nearly full grown, that the fungus produces a 
true decay. When the disease occurs upon the young fruits the 
financial losses may be severe. 



156 FUNGOUS DISEASES OF PLANTS 

The fungus. The mycelium is abundant in the intercellular 
spaces, varying in diameter from 8 to 12 fi, but frequently it is 
of less diameter in the more compact tissue of Vitis vinifera. In 
the leaves the fungous hyphae may be found throughout the part 
affected, except in the woody parts of the bundles of the veins and 
in the stem. They occur also in all tissues except the xylem. The 
haustoria are of the characteristic knob shape. The hyphae are 
somewhat more densely assembled in the vicinity of the stomata, 
and through the stomata there emerge several sporophores (Fig. 
53), each becoming constricted in its passage through the open- 
ing, but subsequently attaining practically normal or more than 
normal diameter, therefore often showing a bulbous base. At 
maturity they are irregularly branched, the central axis giving 
rise to lateral offshoots and sometimes the axis itself may be 
lost, due to the preponderance in growth of the branches. The 
method of branching and sporangial production has been care- 
fully worked out by Farlow, according to whom " the branches, 
which are few in number, generally from four to eight, are 
placed alternately on the upper third of the axis, being generally, 
but not always, distichously arranged. Relatively to the main axis, 
they are all short, the broadest expansion from side to side not 
being usually greater than .12 mm. The branches are furnished 
with branchlets of a second and third order" (Fig. 53, b). 

In this species germination of the zoosporangia takes place 
in water in about one and one quarter hours. The process, as 
summarized from Farlow's careful studies of this phenomenon, 
is about as follows : Spores produced during the night and put 
to germinate during the early morning on slides containing a 
few drops of water show first at the end of an hour the be- 
ginning of segmentation of the protoplasmic contents, each seg- 
ment having a single nucleus. These round themselves off into 
oval bodies, which are massed at the distal end of the sporan- 
gium, and in time they escape by dissolving or rupturing the 
cell wall. The zoospores pass out, generally one at a time, re- 
main quiescent a moment in becoming free, and then swim off 
rapidly, each as a mature zoospore, provided with two lateral cilia, 
projecting usually anteriorly and posteriorly (Fig. 53, c). In gen- 
eral, the zoospores are more or less ovate, but the form in the 



PHYCOMYCETES 



157 



same zoospore may undergo considerable change. The period of 
activity is, as a rule, from fifteen to twenty minutes, at the end of 
which time the resting condition is assumed by the loss of cilia, by 
becoming spherical, and by the development of a cell wall ; then 
follows germination by means of a germ tube. Germination is 
effected practically irrespective of ordinary conditions of light and 
temperature. 

The oospores of this species are not so commonly found as 
the conidiophores. They are more common, apparently, in the 
northeastern states and are generally found upon Vitis cBstivalis. 
They are commonly present during late September and always 
" in the discolored, shriveled parts of the leaves, and are most 
abundant just inside what are called the palisade cells of the 
upper surface." The formation of these oospores is characteristic 
of the family ; that is, large terminal or intercalary swellings of 
the mycelium are cut off by septa, and there results an oogonium. 
In the neighborhood of this oogonium there may be produced 
one or more smaller antheridia. The subsequent development 
of these two structures, the fusion phenomena, and the develop- 
ment of the oospores (Fig. 53, <■/) take place approximately as 
described for Pythunn de Baryanuvi and Cystopiis candidjis. 
At maturity the oospore almost completely fills the original 
oogonium wall, and the wall of the oospore itself is comparatively 
smooth, thick, and yellowish. The oospores measure about 30 /a 
in diameter. For the study of the oospores dried material may 
be teased out in potassium hydrate solution, or it may be neces- 
sary to boil the material in this solution, afterward neutralizing 
with hydrochloric acid. Th-e oospores are set free by the disin- 
tegration of the tissues of the leaf, and they are probably impor- 
tant in carrying the fungus over winter. Nevertheless, much work 
needs to be done in the way of determining to what extent the 
oospores are necessary in the annual propagation of this species. 

Control measures. In the control of this fungus Bordeaux 
mixture is most effective, and it is only during very moist 
seasons, that is, where it is difficult to keep the surfaces of 
the leaves covered with the preparation, that the fungus has 
been able to gain headway in spite of spraying operations. In 
this connection it is interesting to note that copper fungicidal 



158 FUNGOUS DISEASES OF PLANTS 

mixtures first came into use in the treatment of downy mildew 
of the grape. The experiments of Millardet in France in 1881, 
and subsequently, led promptly to the perfection of Bordeaux 
mixture as a fungicide. 



XIII. DOWNY MILDEW OF THE CUCUMBER 
Plasmopara cubensis (B. & C.) Humphrey 

Clinton, G. P. Downy Mildew, or Blight, Peronoplasmopara cubensis (B. & C.) 

Clint., of Musk Melons and Cucumbers. Conn. (New Haven) Agl. Exp. 

Sta. Rept. : 329-362. pis. sg-ji. 1904. 
Farlow, W. G. Notes on Fungi i. Bot. Gaz. 14: 187-190. 1889. 
Humphrey, J. E. The Cucumber Mildew. — Plasmopara Cubensis (B. & C.) 

Mass. Agl. Exp. Sta. Rept. 8: 210-212. 1890. 
Sn<RiNE, F. A., and Stewart, F. C. Spraying Cucumbers in the Season of 

1898. N. Y. Agl. Exp. Sta. Built. 166: 376-396. pis. 1-4. 1898. 
Stewart, F. C. The Downy Mildew of the Cucumber : What it is and how 

to prevent it. N. Y. Agl. Exp. Sta. Built. 119 : 154-183. pis. 1-4. 1897. 

Habitat relations. The two most important diseases of the 
cucumber, or indeed of the commonly cultivated members of 
the gourd family in this country, are the downy mildew and the 
bacterial wilt disease. It has been definitely ascertained that the 
Plasmopara is the chief cause of the poor crops which have 
prevailed in the cucumber districts of New York and a part 
of New Jersey in recent years. The downy mildew of the 
cucumber has an interesting though brief economic history. In 
1869 the fungus was described upon a wild plant found in Cuba. 
It appears that this fungus was not again reported until early in 
the spring of 1889, when it was found in greenhouses in New 
Jersey,^ and by the end of the season it had been detected upon 
the cucumber, squash, and pumpkin in the field in several loca- 
tions in that state. It was further reported during the same season 
from several southern states. Subsequently it developed ^ that the 
fungus had been found in Japan early in the same year. 

This disease-producing organism is now known to occur in 
many sections of the eastern and southern United States, but 
no mention of its occurrence in Europe has as yet come to 
my attention. It is most abundant in regions which have long 

1 Halsted, B. D. Peronospora on Cucumbers. Bot. Gaz. 14 : 149-150. 1889. 

2 Farlow. Notes on Fungi, /. c. 



I 



PHYCOMYCETES 



159 



been devoted to the cultivation of melons or of cucumbers, 
especially for the pickling trade. Nevertheless, it is now a very 
constant disease in greenhouse-grown cucumbers. 

The fungus has been found on most of the cultivated species 
of the Cucurbitaceas, or gourd family, such as cucumbers, musk- 
melons or watermelons, squash, 
pumpkins, gherkin, and also 
upon the star cucumber, Sicyos 
angulatns, and a few other wild 
species. 

Symptoms and effects of the 
disease. The effect of this dis- 
ease upon the host, that is, 
upon the cucumber, have been 
very clearly presented by Stew- 
art as follows : 

The leaves show yellow spots 
which have no definite outline. If 
the weather is warm and favorable 
for the disease, these spots enlarge 
rapidly and run together so that the 
whole leaf becomes yellow and soon 
dies and shrivels like a leaf killed 
by frost. If the weather is cool, the 
yellow spots spread less rapidly. In 
the latter case the central portion of 
the yellow spots becomes dead and 
brittle and of a light-brown color. 
. . . The disease invariably begins 
with the oldest leaves and proceeds 
toward the tips of the vines. Hence the disease appears to proceed from the 
center of a hill outward. In a field recently attacked, the center of every 
hill will be clearly marked by a cluster of yellow leaves, so that the rows may 
be plainly seen clear across the field, even though the plants are large and 
cover the ground. Affected plants continue to grow at the tips and put out 
new leaves, and it is interesting to note how the disease follows at a distance 
of about four or five leaves behind the growing tip. After the disease is 
once thoroughly established, very few cucumbers are produced, although the 
plants may continue to flower profusely. The few cucumbers which are 
formed grow slowly and become misshapen so that they are unsaleable. . . . 
Of the total shortage of 75 per cent, in the Long Island cucumber crop of 1896, 
it is safe to say that 55 per cent, was due to the downy mildew. 




Fig. 54. Plasmopara on Cucumber. 

Salient Phases of Conidial Cycle 

(After G. P. Clinton) 



i6o 



FUNGOUS DISEASES OF PLANTS 



The fungus. The mycelium of this fungus is typical of the 
family. The haustoria have very much the form of those pre- 
viously described for the grape mycelium. The sporophores arise 

through the stomates, 
singly or in small clus- 
ters, and they are 
considerably branched, 
somewhat more flexu- 
ous than those of the 
grape mildew, and the 
fruiting tips are less 
rigid and more widely 
separated one from 
another, corresponding 
more nearly to separate 
branches. The spores 
or zoosporangia are 
slightly violet tinted in 
mass and generally 
ovate in outline. The 
germination of the spore 
has been followed care- 
fully and is known to 
take place by means of 
the characteristic motile 
zoospores. Clinton 
alone has illustrated the 
various stages of germi- 
nation (Fig, 54, r and d). 
Fig. 55. Peronospora on Young Cabbage Leaf Occasionally the normal 

sporophores are accompanied by short, swollen hyphse (Fig. 56, b), 
which may also bear spores. It is believed that the latter are pro- 
duced under unfavorable conditions, and similar modifications have 
been noted in other species. The oosporic form of this species has 
not yet been found, and it is doubtful if it occurs in this country. 

Control. Very careful experiments have been made with a view 
to holding in check the ravages of this fungus, and it has been 
found that the greater part of the damage can be prevented by 




PHYCOMYCETES l6l 

properly spraying with Bordeaux mixture. Seven sprayings in 
New York have almost invariably enabled growers to control this 
disease. The 5-5-50 formula may be recommended. 

Plasmopara Halstedii Farl. is widely distributed in the United 
States, where it is found on various members of the Compositae, 
especially sunflower and Jerusalem artichoke, HeliatttJms aiimuis 
and HeliantJms tuberosiis, species of Bidens, etc. 

XIV. SCLEROSPORA 

CuGiNi, G., and Traverso, G. B. La Sclerospora macrospora Sacc. parasita 
della Zea Mays. Le Stazioni speriment. agrar. italiane. 35 : 46-49. 

Traverso, G. B. Note critiche sopra la Sclerospora parassite di Graminacee. 
Malpighia. 16: 280-290. 1902. 

There are perhaps three species of this genus. The species 
which has been apparently most widely distributed and best 
known is Sclerospora gnnninicola (Sacc.) Schroet. This species 
occurs upon several grasses, especially Setaria spp. The leaves 
are affected, and in severe attacks they may be considerably 
rolled and shredded. The conidiophores are relatively evanes- 
cent. They are irregular in form and generally nodulose, or of 
irregular diameter, generally short, branched, and slightly colored 
with conidia 12-20 x 10-18 /x. The oospores are at first densely 
granular and hyaline in appearance, later they are slightly colored, 
thick-walled, united with wall of oogonium, and angularly glo- 
boidal, usually 40-42 /i in diameter. Another important species, 
Sclerospora macrospora Sacc, formerly known only on a few true 
grasses, has more recently been found to be the cause of an im- 
portant disease of corn in Italy. The tassel is the chief seat of 
infection. Fairchild reports this fungus from the United States. 
In this species conidiophores are unknown, and the oospores are 
about 60-65/11 in diameter. 

XV. DOWNY MILDEW OF CRUCIFERS 

Pero7iospora parasitica (Pers.) De Bary 

Wager, Harold. On the Fertilization of Peronospora parasitica. Ann. 
Bot. 14: 263-279. pi. 26. 1900. 

This fungus seems to be particularly abundant in England, but 
it is also found in other parts of Europe and in the United States. 
Practically all cultivated Cruciferae are more or less subject to it, 



l62 



FUNGOUS DISEASES OF PLANTS 



as well as many wild species. It frequently causes stem deformi- 
ties, and in England it is often associated with Cystopiis candidiis 

on Capsella, while in this 
country it is perhaps best 
known as a pest in cauli- 
flower culture under glass, 
yet occasionally destructive 
in cabbage cultures in the 
open, and less frequently 
occurring on radish, turnip, 
etc. 

The conidiophores, shown 
in Fig. 56, a, are character- 
istic of the genus. The co- 
nidia germinate (Fig. 56, b) 
from one side by means of a germ tube. The development of the 
oospores of this species has been carefully studied and would 
correspond closely to that described for Cystopiis caiididiis except 
that in this Peronospora there is no true coenocentrum. 




Fig. 56. Peronospora on Cabbage: 
CoNiDiAL Stage 



XVI. ONION MILDEW 

Peronospora ScJdcidcuiana De Bary 

Thaxter, R. The Onion Mildew. Conn. Agl. Exp. Sta. Kept. (1889): 

155-158. 
Trelease, Wm. The Onion Mold. Wis. Agl. Exp. Sta. Kept. (1884): 38-44. 
Whetzel, H. H. Onion Blight. Cornell Agl. Exp. Sta. Built. 218 : 138-161. 
figs. I -1 7. 1904. 

The onion mildew, blight, or mold is a disease which has 
been recognized for more than half a century. At various times 
since 1884 it has been reported as of consequence in parts of 
the United States from New England to Wisconsin. It is proba- 
bly far more common and destructive than has been supposed, as 
shown by the observations of Whetzel in 1903. 

The disease, in the regions referred to, appears in late June or 
July, and in the early morning while covered with dew it is in 
young stages conspicuous by a "furry violet appearance" of the 
affected leaves. Later the leaves become moldy in character, pale, 
collapsed, and often broken. Fig. 57 shows a diseased plant in 



PHYCOMYCETES 



i6- 



an acute stage. Older onions are apparently more susceptible 
than young, and recovery in the former case is seldom. 

The fungus. The mycelium is considerable, and it penetrates 
practically all parts of the leaf. The minute haustoria are numerous, 




Fig. 57. Onion Mildew 
(Photograph by H. II. 
Whetzel) 



Fig. 58. Mature Conidiophore, Germinat- 
ing CONIDIUM, AND MYCELIUM OF ONION 

Peronospora. ((- after Whetzel) 



thread-like, and often branched at the tip. The conidiophores 
arise through the stomates. They are of the characteristic type, 
often 320 fx, in height, and bear large elliptical conidia (44-52 x 
22-26 /x) which germinate promptly by a side tube and effect 
penetration through the stomates. The time required for infec- 
tion and the production of conidiophores again is extremely 



1 64 FUNGOUS DISEASES OF PLANTS 

short, so that the fungus spreads with great rapidity. Oospores 
are commonly produced. 

Control. It would seem that this fungus has been controlled 
in New York by systematically spraying where it is likely to be 
abundant after June 15. In addition, however, it is important to 
destroy the tops of diseased plants, and by no means to return 
these to the land or throw them on the compost heap, since the 
oospores retain their vitality a long time. Rotation of crops is 
also important. 



XVII. PERONOSPORA: OTHER SPECIES 

Peronospora sparsa Berk, is not an uncommon parasite of 
cultivated roses in Europe. At times it has been productive 
of serious epidemics. Affected leaves show brown spots on the 
upper surfaces not unlike the blotches produced by other fungi, 
but on the under surfaces the repeatedly dichotomous conidio- 
phores appear in sufficient quantity to be readily recognized as 
a mildew. 

Peronospora effusa (Grev.) Rabh. develops during moist weather 
a destructive disease of spinach {Spinacia oleracca), and it is also 
common upon other members of the Chenopodiacese, as well as 
upon certain Plantaginaceae. Pale or water-soaked spots are pro- 
duced and the leaves may be rapidly killed. Ordinarily oospores 
are found in quantity. 



XVIII. DOWNY MILDEW OF THE LETTUCE 

Bremia iMctuac Reg. 

Downy mildew of the lettuce is not an infrequent pest where 
lettuce is grown under glass during the winter and spring. It 
also occurs with cool weather in the open, particularly upon fall 
lettuce. This fungus is also quite generally distributed on several 
species of Senecio, Sonchus, and Lactuca as well as on a few 
other species of Compositse. Upon lettuce the conidiophores of 
the fungus appear on the under side of the leaf, and the areas 
affected are at first merely paler in color, afterwards wilting. 



PHYCOMYCETES 



165 



The conidiophores appear singly. They are 
much branched and near the apices of the 
branches at maturity pecuhar disk-hke swelhngs 
are produced, each of which originates circum- 
ferentially about four tentacular tips inclined out- 
ward so as to continue more or less the general 
direction of the branch axis. Ovate conidia meas- 
uring 16-22 X I 5-20 /x are produced singly, and 
these germinate readily in water, emitting a germ 
tube through an apically developed pore (Fig. 59). 
Oospores are occasionally found. These are small, 
26-35 /i in diameter, light brown, and roughened. 
In controlling this fungus general sanitary pre- 
cautions must be taken and a maximum of light 
and ventilation should be constantly afforded. 




XIX. THE LATE BLIGHT AND ROT OF THE POTATO 
Phytophthora infestans (Mont.) De Bary 

Clinton, G. P. Downy Mildew, or Blight, Phytophthora infestans (Mont.) 
De By., of Potatoes. Conn. (New Haven) Agl. Exp. Sta. Rept. (1904): 
363-384. pis. 32-3-/. Ibid. ([905): 304-330. ph. 23-23. 

De Bary, A. Recherches sur le developpement de quelques champignons 
parasites. Ann. d. Sci. Nat. Bot. 20 (4me Ser.): 1-148. pis. 1-13. 
1876. 

De Bary, A. Researches into the Nature of the Potato Fungus — Phytoph- 
thora infestans. Journ. Roy. Agl. Soc. 12 (2d ser.): 240-269. Jigs. 
1-8. 1876. 

Jones, L. R. Certain Potato Diseases and their Remedies. Vt. Agl. Exp. 
Sta. Built. 72: 13-16. 
(Short accounts also in several earlier bulletins and reports.) 

Jones, L. R. Disease Resistance of Potatoes. Bureau Plant Ind., U. S. Dept. 
Agl. Built. 87: 1-39. 1905. 

Stewart, F. C, Eustace, H. J., and Sirrine, F. A. Potato Spraying Experi- 
ments in 1906. N. Y. Agl. Exp. Sta. Built. 279: 154-229. pis. 1-2. 
Jigs. 1-4. 1906. (Cf., also, Bulks. 290, 307, and 311.) 

Stuart, Wm. Disease Resistance of Potatoes. Vt. Agl. Exp. Sta. Built. 122 : 
107-136. 1906. 

Ward, H. Marshall. Diseases of Plants. The " Potato Disease," Chapt. 5 : 
59-85. 1896. London. 

The late blight and rot of the potato is so generally known 
that frequently this malady is simply called the " potato disease." 
From an economic point of view it is the oldest potato malady, 



1 66 



FUNGOUS DISEASES OF PLANTS 



and it has been the cause of great disaster in many potato-growing 
regions before methods for its control were well known. All who 
are familiar with the history of potato growing doubtless know of 
the potato famine of 1 845. The serious famine in Ireland was very 

largely due to this failure of the 
potato crop, a failure due to the 
prevalence and unusual destruc- 
tiveness of the Phytophthora. 

Distribution. At one time it 
was the current opinion that this 
fungus is very widely distributed 
throughout the United States, 
but a more careful study of po- 
tato diseases has shown that it is 
very largely limited to New Eng- 
land and New York, extending 
also into the potato-growing re- 
gions of Canada. It is not en- 
tirely absent from regions much 
farther south and west, but in 
such districts it seldom assumes 
any importance. In Europe it 
is widely distributed and may 
be disastrous throughout Great 
Britain, as well as east and west 
from Russia to Erance, extend- 
ing even as far south as Italy. The distribution of this fungus and 
its importance as a disease organism are entirely dependent upon 
climatic conditions. It has been shown that it becomes of seri- 
ous importance only when favored by warm, moist weather. As 
a rule, the fungus does not appear in the northeastern United 
Stiites prior to the last days of July, and it is most abundant 
during August and early September. A few days of rainy 
weather suffice to give it a start and to bring to fruiting the 
conidial stage on the leaves. The distribution of the fungus 
is then accomplished with alarming rapidity, and whole fields 
may be devastated within a period covering only a few days 
of such weather. While it is generally stated that warm weather 




Fig. 60. 
Leaves. 



Phytophthora on Potato 
(Photograph by F. C. Stewart) 



PHYCOMYCETES 



167 



is required, it has also been shown that the high temperature of 
summer quickly checks its spread. 

Symptoms. Upon the leaves of the potato this fungus de- 
velops characteristic spots which cannot be easily confused with 
other potato diseases. These spots frequently begin at the edge 
or tip and spread until the whole leaf may be involved. They 
present in moist weather a dark, 
somewhat water-soaked appear- 
ance with slightly purplish tint 
(Fig. 60). In drier weather they 
are brown without the definite 
markings of the early blight. 
The moist appearance of the 
spots accompanied by the wilt- 
ing of the leaf, or of that por- 
tion affected, offers an easy 
diagnosis. Generally there is 
no accompanying stem injury, 
but in some cases the trouble 
may extend to the stem ; or, 
again, it may be found upon 
the leaves as an extension of a 
stem affection. Upon the tubers 
this fungus develops the well- 
known dry rot (Fig. 61). On Fig. 61. The Phytophthora Disease 

account of the presence of the '^^ P^"^-^™ 'T"^^'^'- (Photograph by 

. , . , . r F- C. Stewart) 

mycelium withm the tissues of 

the tuber the cells are killed and the tubers rendered liable to 
the ordinary forms of wet rot induced by bacterial action or by 
mold fungi. The dry rot may cause serious damage in the field, 
yet this damage may be further emphasized or even first made 
evident while the potatoes are in storage. In regions which are 
favorable no fungous disease may become more quickly disastrous, 
particularly when it affects the tubers as well as the vines. Fortu- 
nately it is now feasible to prevent the disease and possible even 
to stamp it out. 

Host resistance. P'or more than half a century the resist- 
ance of varieties of potatoes to the late blight has received the 




l68 FUNGOUS DISEASES OF PLANTS 

attention of scientists. The early work was remarkable for its 
time, but the actual results accomplished lose their value now 
on account of the fact that the older varieties have largely dis- 
appeared from cultivation. Excellent work was done during the 
early part of 1 870-1 880, when Charles Darwin himself became 
much interested in resistance breeding, 187 2- 1878. As a result 
of the interest which was then established, the various wild 
species of potato growing in South America were carefully studied 
with reference to this point and numerous crosses and selections 
made. Again, during the past ten years there has been a re- 
vival of interest in this subject, and to-day the general problem 
is better understood and the results will probably be more lasting. 
It may be said, however, that while many varieties have been de- 
veloped which show a considerable degree of resistance, yet it is 
also true that no variety may be expected to maintain such resist- 
ance throughout a long period of time. Gradually there will be 
deviation from the original sort, and, moreover, its relation to the 
particular environments in which grown will doubtless also affect 
the relations to the blight organism. 

It cannot be expected that a single variety will be equally re- 
sistant under different conditions. Therefore, in diverse localities 
and particularly in different regions variations will be apparent. 
The studies which have thus far been made upon resistance have 
concerned both foliage and tuber resistance. According to the 
experiments in Vermont (Stuart) Rust Proof was most resistant 
in 1903, so far as the foliage is concerned, and the Dakota Red 
was second; while in 1904 the order was as follows: Monterey, 
Solamini Coinnicrsonii, Solannm polyadcnium, Rust Proof, Sut- 
ton's Discovery, June, Mexican, Mammoth Gem, and Manum's 
No. 3. With relation to tuber resistance Dakota Red has made 
the best showing for two seasons, although it was not wholly free 
from rot. The other varieties which show least blighting of the 
foliage were also resistant to the rot. The following interesting 
summary has been drawn : 

1. Some varieties are less subject to vine injury than others. 

2. Some show a greater tuber resistance to rot than others. 

3. With some there seems to be a fairly close relation between 
resistance of vine to disease and of the tuber to rot. 



PHYCOMYCETES 



169 



4. Selection has not given visible increase of resistance. 

5. Hybridization and the growing of seedling plants, followed 
by careful selection, seem to offer a more logical method of se- 
curing disease-resistant varieties than does selection. 

The tomato is occasionally subject to this disease, but so far as 
is now known it is not seriously affected in any part of the world. 

The fungus. The mycelium 
of the Phytophthora, like that 
of the other members of this 
family, is unicellular, and the 
haustoria are filamentous. The 
conidiophores arise singly or in 
groups of from two to four 
from the stomates. The conidio- 
phore is branched, and at the 
tip of each branch a conidium 
is produced. The conidium is 
pushed to one side and the 
branch continues. The continua- 
tion is, however, larger than the 
tip which produced the conid- 
ium, so that this further growth 
is marked by an enlargement 
of the branch, making a very 
characteristic form of conidio- 
phore (Fig. 62). The conidia are 
ovate and usually measure 27- 
30 X 1 5-20 fi. The conidia ger- 
minate readily when fresh, by the 
production of about eight zoo- 
spores. Germination may be 
secured in water but apparently not in nutrient solutions. The 
zoospores are motile for a brief time, perhaps seldom longer 
than a hour. They then come to rest and appear spherical and 
invested with a wall. Germination readily follows, and the germ 
tube penetrates the leaf either by stomates or by boring through 
the cuticle. The conidia serve not only to spread the disease 
rapidly from leaf to leaf, but they also fall upon the soil and may 




Fig. 62. Section of Potato Leaf 
And Conidiophores of the Phy- 
tophthora 



170 



FUNGOUS DISEASES OF PLANTS 



be brought in contact with tubers. They penetrate the tubers as 
readily as the leaves, the dry rot being produced in consequence. 
An affected tuber which does not show the disease in severe 
form may be used as seed, and thus the disease may be propa- 
gated from year to year through the seed tubers. It is now 
quite certain that the perennial appearance of the disease is due 
to this use of diseased tubers. It is not always possible, how- 
ever, to determine if the mycelium is present in the tubers, since, 
even though they may have been stored for many months, the 




sprayi:d 



'" sprXyed 

3 TIMKS 



Fig. 63. Control of Late Blight of Potatoes by Bordeaux Mixture 
(Photograph by F. C. Stewart) 

fungus will not develop further if the conditions are unfavorable. 
Thus if stored at a low temperature and in a dry atmosphere the 
rot fungus may not become evident. No oosporic stage of the 
Phytophthora has been found, and it is believed that this stage 
has become lost and is now wholly unnecessary in the life cycle 
of this species. 

Control. Studies looking toward the prevention of the potato 
blight were begun during the middle of the past century. At 
first the greatest success was accomplished only in securing 



I 



PHYCOMYCETES I 7 1 

comparatively resistant sorts. Soon after the discovery of Bordeaux 
mixture, and more than thirty years ago, this fungicide was effect- 
ively used as a preventive of the late blight. By repeated experi- 
ments under a variety of conditions it has now been abundantly 
shown that the proper use of Bordeaux mixture will, in ordinary 
seasons, hold this disease in check, reducing its ravages to a small 
minimum (compare Fig. 63). It is ordinarily advisable to begin 
spraying with 5-5-50 Bordeaux when the plants are about six 
inches high, and at least three thorough applications from ten days 
to two weeks apart are advised. In some cases two additional 
applications may be necessary. Again, it should be remembered 
that the fungus is carried over winter largely, or perhaps entirely, 
by a hibernating mycelium in the tubers, and that every effort 
should be used to secure seed potatoes from a field in which no 
blight or rot has occurred. If this latter could be done in connec- 
tion with a system of rotation, there is no apparent reason why 
the disease might not be practically stamped out in any con- 
siderable region. 

XX. DOWNY MILDEW OF LIMA BEANS 
Phyfophthora Phaseoli Thaxt. 

Clinton, G. P. Downy Mildew, PliytopJiihora Phaseoli Thaxt., of Lima 

Beans. Conn. Agl. Exp. Sta. Rept. (1905): 278-303. ph. 20-22. 
Halsted, B. D. The Downy Mildew of Lima Beans. N. J. Agl. Exp. Sta. 

Built. 151: iS-24. Jigs. 6-g. igoi. 
Sturgis, W. C. The Mildew of Lima Beans (Phytophthora Phaseoli Thaxt.). 

Conn. Agl. Exp. Sta. Rept. (1897): 159- 166. (Also Bot. Gaz. 25: 191- 

194. 1898.) 
Thaxter, R. Mildew of Lima Beans (Phytophthora Phaseoli Thaxt.). Conn. 

Agl. Exp. Sta. Rept. (1889): 167-171. 

Occurrence. Since the discovery of this fungus, in 1889, near 
New Haven, Conn., it has been, nearly every year, of sufficient 
importance to merit special attention in some one or more of the 
North Atlantic States, and it is also reported from Russia. It is 
found upon dwarf and pole sorts of the lima bean, Phaseohis 
lunahis, and has been reported on no other host. The fungus is 
more commonly observed upon the pods, but it also attacks buds, 
leaves, and shoots. Upon the pods conspicuous patches of the white 
conidiophores are produced, mostly on the side least protected 



172 FUNGOUS DISEASES OF PLANTS 

by the vine. Pods badly affected may wilt and die, and the fungus 
may penetrate to the seed. 

Moist seasons are most favorable to the production and spread 
of this disease. Sturgis has determined an interesting relation of 
this fungus to insects. Bees and other insects visiting the blos- 
soms of the beans may come in contact with the basal portion 
of the style and the basal portion of the ovary, corresponding to 
the two ends of the pod. Observation indicates that it is at these 
points primarily that the fungus begins its work. Rain is also 
effective in rapidly spreading the spores. 

The fungus. The mycelium is irregular in diameter, siphon- 
aceous when young, and often empty and septate when old. The 
conidiophores are produced in great numbers. They are upright, 
considerably branched near the bases and longer than those of 
other species of the genus. They form on the surface a matted 
mass, and it is possible that threads of the mycelium proper may 
also develop superficially. The conidia, produced much as in the 
previous species, are large, measuring generally 28-42 x 17-27/i, 
with a distinct germinal papilla. Fresh spores germinate readily, 
and generally by the production of biciliate, fusiform zoospores. 
Germination may also occasionally proceed by means of a germ tube. 

Oospores of this fungus were not found until 1905. According 
to Clinton, " Judging from the experience of the past year, the 
oospores should be looked for toward the end of the season and 
in the seeds of the pods badly infected with the mildew." It is 
believed that the production of oospores is frequently interfered 
with by the rapid growth of saprophytic fungi. The oogonia are 
inter- or intra-cellular, rather thick-walled, smooth^ and generally 
19.5-22.5 /i in diameter. 

By carefully removing the seeds from infected pods, Clinton 
was able to grow this fungus in pure cultures on such seeds, and 
likewise on nutrient media containing agar, corn meal, etc. Both 
conidia and oogonia were produced. 

Control. On a small scale spraying experiments with Bordeaux 
mixture have been successful. It is important, however, that only 
seed from clean pods should be used. Rotation of crops is required 
wherever oospores are produced, and under such circumstances, 
also, the destruction of all diseased parts is equally valuable. 



PHYCOMYCETES 1 73 

Phytophthora cactorum (Leb. & Cohn) Schroct. This species 
of Phytophthora, if it is a single species, shows as great a range 
of host plants as the common damping-off fungus, Pythuim dc 
Baryannm. It was first described as a disease of certain Cactaceae 
grown under greenhouse conditions, also of succulent species be- 
longing to the genus Sempervivum. Hartig^ and other forest 
botanists have found it to be one of the most disastrous fungi 
known upon seedlings of such trees as the pine (Pinus), beech 
(Fagus), and many others. Additional hosts among herbaceous 
plants have also been well established, and the fungus may be 
regarded as unusually widespread and important. The conidia 
(zoosporangia) are unusually large, often averaging 60 /* in di- 
ameter. Upon germination numerous zoospores are produced. 
Oospores are present in this species. These are small, often 
24-30 /i. 

1 Hartig, R. Der Buchenkeimlingspilz, Phytophthora Fagi, m. Unters. a. d. 
forstbot. Institut, Miinchen. 1 : 33-57. pi- 3- 1880. 



CHAPTER XI 

ASCOMYCETES 

The Ascomycetes, the largest class of the fungi, containing 
approximately half of all the described species, have perhaps 
one common characteristic, — the ascus, or spore sac, generally 
with a definite number of spores (ordinarily eight). The ascus 
is of many types and may be produced in a variety of ways, 
sometimes apparently in a manner analogous to simple spo- 
rangia ; again, it may be formed upon the surface of, or within, 
more or less complex fruit bodies. The fruit bodies, in turn, may 
be within or upon a modified mycelial tissue, termed a stroma. In 
some cases the fruit body and asci arc developed after cell and 
nuclear fusion in special organs, phenomena indicating sexuality. 
The size, form, and consistency of the fruit bodies are extremely 
diverse, examples of these diversities being well borne in mind 
by a comparison of the large edible morel with the minute fmit 
bodies (perithecia) of the lilac mildew. 

Nonsexual, or conidial, spore forms of manifold variety are 
known, and a single species may possess several of these forms. 
In general, the mycelium is considerable, exposed or imbedded 
in the substratum, septate, and relatively thick-walled. Some 
orders contain only a few and others many parasitic species. 

As usually considered, the Ascomycetes include about ten orders 
and more than sixty families. For convenience, two subdivisions, 
with rather artificial limitations, may be recognized in this class 
among those with definite fruit bodies, namely, (i) the Dis- 
comycetes, in which the asci are produced in a body finally open- 
ing more or less as a cup-shaped or saucer-shaped apothecium ; 
and (2) the Pyrenomycetes, in which the asci are developed 
within a perithecium, or an enveloping structure, which may be 
entirely closed, or open by a relatively small mouth, the ostiolum. 

174 



ASCOMYCETES 1 75 

The families of the Discomycetes (or discomycete-hke forms) 
which are here of interest are Exoascacese, Helotiaceae, Mol- 
Hsiaceae, and Phacidiaceae. The Pyrenomycetes from which im- 
portant parasitic representatives have been selected are the 
Perisporiaceae, Erysiphaceae, Hypocreaceae, Dothidiaceae, Myco- 
spherellaceae, Pleosporaceae, Gnomoniaceae, and Diatrypaceae. 

I. EXOASCACE^ 

Atkinson, G. F. Leaf Curl and Plum Pockets. Cornell Univ. Agl. Exp. Sta. 

Built. 73: 319-355. pis. 1-20. 1894. 
Patterson, Flora W. A Study of North Am. Parasitic Exoasceas. Labs. 

Natural Hist, Univ. of Iowa Built. 3: 89-135. pis. 1-4. 1895. 
Rathav, E. Ueber die Hexenbesen der Kirschbaume und liber Exoascus 

Wiesneri n. sp. Sitzber. d. kaisl. Akademie d. Wiss. 83 : 267-288. pis. 

1,2. 1881. 
Robinson, B. L. Notes on the Genus Taphrina. Ann. Bot. 1 : 163-176. 

1887. 
Sadp:beck, R. Die parasitischen Exoasceen. Eine Monographic (Arb. d. bot. 

Museums zu Hamburg). 1893. 
Sadebeck, R. Einige neue Beobachtungen und kritische Bemerkungen iiber 

d. Exoascaceas. Ber. d. deut. bot. Ges. 13: 265-2S0. pi. 21. 1895. 
ScHROETER, J. Exoascaccas. Pflanzenfamilien (Engler u. Prantl) 1 (i* Abt.): 

158-161. fig. 136. 1894. 

The Exoascaceas are parasitic fungi causing slight or very 
marked abnormalities of the leaves, fruits, etc., of a variety of 
plants, mostly woody forms. The deformities are commonly of 
the nature of leaf curls, malformed fruits (such as plum pockets), 
and witches' brooms. Such diseases are especially common among 
the stone fruits. This family of fungi is considered by many to 
be closely related to the lowest Discomycetes. In the Exoas- 
caceas, however, the asci are produced on the surface of the host, 
arising directly from the mycelium, without the development of 
a distinct, complex, basal structure, or hymenial layer. Each ascus 
may possess a stalk cell or it may be merely cut off by a cross 
wall from a hypha growing perpendicular to the surface. An 
ascus usually contains eight spores, which in some cases bud ex- 
tensively in a yeast-like manner, even within the ascus. 

In the genus Exoascus, which embraces those forrns of greatest 
economic importance in the family, there are almost constantly 
eight spores, and budding seldom occurs prior to the expulsion 
of the spores from the ascus. 



176 FUNGOUS DISEASES OF PLANTS 

II. PEACH LEAF CURL 
Exoascus deformafis (Berk.) Fuckel 

DuGGAR, B. M. Peach Leaf Curl. Cornell Agl. Exp. Sta. Built. 164: 371- 

388. figs. 66-y2. 1899. 
Pierce, N. B. Peach Leaf Curl : Its Nature and Treatment. Div. Veg. Path. 

and Phys., U. S. Dept. Agl. Built. 20: 1-204. P^^- i-JO- 1900. 
Selby, a. D. Preliminary Report upon Diseases of the Peach. Ohio Agl. 

Exp. Sta. Built. 92 : 226-231. 1898. 
Selby, A. D. Variation in the Amount of Leaf Curl of the Peach (Exoascus 

deformans) in the Light of Weather Conditions. Proc. Assoc. Prom. 

Agl. Sci., Ann. Meeting 20: 98-104. 1899. 

Peach leaf curl {Krduselkrankhcit in Germany ; Cloqnc dn 
pechcr in France) is an important fungous disease affecting par- 
ticularly the leaves and tender shoots of the peach, but injuring 
likewise, occasionally, the flowers and fruit. 

Distribution. Attempts to determine the country which might 
be regarded as the original home of this fungus have proved 
wholly futile. Leaf curl is now a more or less common disease 
in nearly all peach-growing regions of the world. In North 
America it is known throughout the country, at least east and 
west, and from northern Canada to the Gulf of Mexico ; while 
in South America it has also been reported from several peach- 
growing districts. In Europe it has long been common, having 
been reported in England as early as 1821, and it is disastrous 
in many sections of China and Japan. This disease occurs also 
in southern Africa, and from the Sahara northward in Algeria. 
According to reports it prevailed in Australia even in 1856, and 
it has proved most pernicious to peach-growing interests in New 
Zealand, In general, therefore, this disease is known wherever 
peach growing is practiced. In the United States the general 
regions in which the more serious and constant injuries have 
been felt are apparently two, viz., the region of the Great Lakes 
and the Pacific Slope region, the latter including also districts in 
central and northern California. 

Climatic relations. Plant pathologists are almost unanimous in 
the assertion that this fungous disease is most prevalent and most 
disastrous when the spring is cold and damp. Practical orchardists 
likewise concur in this opinion. Pierce about ten years ago col- 
lected statistics from about one hundred orchardists bearing upon 



ASCOMYCETES 



177 



this point. Ninety-two per cent believed that a cold spring is 
favorable to the disease ; more than seventy-five believed the wet 
weather also to be a factor. Six and seventeen per cent, respec- 
tively, expressed opinions opposing the view that cold and mois- 
ture are influencing factors. The memorable leaf-curl years in 
New York and Ohio, 1893, 1897, and 1898, were preceded by 




Fig. 64. Peach Leaf Curl 

cold and humid conditions during April, the time when the buds 
normally start. On the other hand, there is no record that the 
peach leaf curl has ever been particularly destructive during a 
warm and relatively dry spring. So firm is the opinion of a few 
of the practical growers as to this climatic relationship that they 
refuse to believe anything more than that the weather is the direct 
cause of the leaf curl. Moreover, heavy dews appear to be of in- 
significant environmental importance, and in view of the conditions 
developing dew, this would be anticipated. 



178 FUNGOUS DISEASES OF PLANTS 

Losses. The losses from leaf curl may not be so readily esti- 
mated as with many other fungous diseases, for the injury to the 
fruit is usually indirect, through the loss of leaves and the gener- 
ally impaired vitality of the tree. Before the adoption of any 
rational preventive measures the losses in the United States were 
estimated at about three million dollars. In general, heavy losses 
in the South, on the Atlantic seaboard, and in the Southwest are 
infrequent, yet occasionally the damage is severe ; while in the 
two regions previously mentioned as more severely visited, the 
losses are more nearly annual, and the entire crop may occa- 
sionally be destroyed. 

Symptoms. The idea generally prevails that the leaf curl oc- 
curs only upon leaves and young branches, but the flowers and 
young fruit are likewise subject to attack. Since in the latter case 
the deformations are less conspicuous, and dropping of the parts 
affected is more prompt, it has often escaped attention. Leaves 
of the peach affected by this fungus may be detected as soon as 
the leaf buds have become slightly upfolded. The coloring of the 
young leaves is somewhat heightened, and as they unfold a curl- 
ing and arching of the blades becomes prominent. The distortion 
may be confined to a small area on one leaf as one extreme, or it 
may occur on all leaves and petioles, as well as on the young stem 
which bears these (Fig, 64). As the leaves mature the green or 
reddish color is lost and the hypertrophied areas become pale or 
slightly discolored. Diseased shoots may attain more than twice 
their normal diameter and become pale in color. Further changes 
in the external appearance have been noted in a gray or mealy 
appearance of the surface, which occurs as a result of the produc- 
tion of the fungus superficially. Later the affected leaves turn 
brown and are finally defoliated. When defoliation is extensive 
the fruit crop will either be lost entirely or so stunted as to be of 
little value. Under favorable conditions a new crop of leaves will 
be promptly developed, but there is little or no evidence that this 
second crop of leaves may be affected even to a very limited ex- 
tent. Gummy exudations sometimes appear on the enlarged twigs, 
particularly when the enlargement is not terminal. In case the 
terminal bud is not affected it may continue to grow later in the 
season, thus leaving the injured or swollen portion at the base of 



ASCOMYCETES 



179 



the new growth. It was formerly supposed that this fungus was 
very largely propagated by a perennating mycelium, or by infec- 
tions resulting during the summer and persisting in the woody 
parts until the following season, but as will be shown later, infec- 
tions must generally occur as the buds unfold. The percentage 
resulting from a mycelium remaining alive in the hypertrophied 
twigs is very small. The badly affected twig dies and the my- 
celium with it. From other affected twigs diseased leaf buds are 
seldom produced (Fig. 65), 




Fig. 65. One Healthy and Three Diseased Twigs of Peach; the 
Center Twigs recovered from the Attack 

Susceptibility of host varieties. There is a great difference in 
the susceptibility of different varieties under similar conditions. 
Moreover, a single variety may show a difference in resistance 
when grown under diverse environmental conditions. A list of 
the most susceptible varieties in New York would not correspond 
with a list for California, Among susceptible varieties in the far 
West have been included such as the following : Crawford's 
Early and Late, Elberta and Salway, Heath King and Hale's 
Early, Lovell, Old Mixon Free, etc. ; while for Ohio, Mountain 
Rose, Old Mixon, Globe, Elberta, and others are among those 
most affected. 



l8o FUNGOUS DISEASES OF PLANTS 

A striking correlation seems to obtain between the serration 
of leaves and susceptibility to curl, the serrate varieties being 
very slightly susceptible as compared with those which have the 
glands of the leaves reniform or globose. Other interesting rela- 
tionships have been suggested. 

The fungus. While the leaf curl has evidently been known 
in England as a peach disease since 1821 or earlier, the fungus 
was first described by Berkeley in 1857. It has therefore been 
known to botanists for half a century. Infection takes place at 
the time of the opening of the buds (most frequently), but it may 
also result (occasionally) by the growth of a perennial mycelium 
from the old wood, in which it has rested over winter, into the 
expanding peach buds. According to Sadebeck, the mycelium 
winters over in the primary cortex and medullary tissues of the 
one-year-old branches. 

In order to examine the mycelium to the best advantage a 
section should be made of a leaf or twig before the fungus has 
appeared upon the surface. The distribution of the mycelium 
within the host tissues may then be more easily followed, owing 
to the greater protoplasmic content. A microscopical study of 
hand or microtome sections indicates that the intercellular my- 
celium is quite generally distributed in the parenchyma of the 
leaf and in the cortex of the young stems. Three types of my- 
celium have been recognized (Pierce), and these may be detected 
in leaf or in shoot : 

1. The most common type is designated vegetative hyphce. 
These are very diverse, both in the diameter of the tubes and 
in the character of the branching, as shown in Fig. 66, b. Ad- 
jacent cells are separated by peculiar plate septa. 

2. The second class of hyphse are known as distj-ibntive JiypJuc, 
and these are in the main composed of long cells of more or less 
uniform diameter, coursing, for the most part, parallel to the stem 
axis, and they are found abundantly in the pith or beneath the 
epidermal cells (Fig. 66, c). 

3. Fruiting hyphce. The vegetative hyphae which have devel- 
oped beneath the epidermis push up between the epidermal cells, 
and there is formed between the upper edges of the epidermal 
cells, and also between the epidermis and the cuticle, an extensive 



ASCOMYCETES 



l8l 



development of short, modified hyphal cells (Fig. 66, d). lliese 
are properly the ascogenous cells, which by an abundant budding 
process form frequently an almost continuous layer beneath the 
cuticle. The asci develop from these ascogenous cells, as upward 
prolongations, pushing through the cuticle, while the original 
ascogenous cell is finally cut off by a cross wall as a stalk or foot 




Fig. 66. Exoascus on Peach: Asci, Germinating Si'ores, and Hyph,b 
{l>, f, and </ after Pierce) 

portion. The ascus is usually somewhat truncated at the apex and 
densely filled with protoplasm. It may measure 25-40 x S-h/m 
(ave. 30-35 X 9-10). As a rule it contains at maturity eight 
spores, although the number may vary from four to eight (Fig. 
66, a). These asci often arise in such numbers that they form prac- 
tically a continuous palisade-like layer over the fruiting surface. 

The ascospores may bud before being thrown out of the ascus, 
but as a rule the spores are forcibly ejected from the ascus at 
maturity. Budding results in the successive production of conidia, 



1 82 FUNGOUS DISEASES OF PLANTS 

which may therefore be termed primary, secondary, etc. These 
conidia may be propagated for some time in beerwort. On the 
host germination may proceed normally, that is, by the direct pro- 
duction of a true germ tube ; moreover, germination rather than 
budding is occasionally observed in culture. The grayish cast 
given to the surface of the leaf is due to the numerous asci, and a 
mealiness may become evident later from the abundance of conidia. 

Infection. Since, as shown later, the disease may be in very 
large part prevented by spraying prior to the opening of the 
buds, it is evident that infection would seem to result, in general, 
by spores or conidia which have been caught in the bud scales, 
or, at any rate, which were adherent to the buds at the time of 
opening. It is therefore believed that the marked effect of con- 
ditions upon the prevalence of the leaf curl is brought about in 
this way : During cold, moist weather the young leaves within 
the bursting buds would be in a state described as suffused with 
water, and consequently attended by lowered vitality. The fungus 
would therefore gain entrance more readily. If, however, at this 
time the bud scales were well covered with a toxic fungicide, the 
germ tubes of the fungus would in most cases fail to cause infec- 
tion. Again, the effect of conditions does not end with infection, 
and it is well known that the extent of the disease upon single 
leaves or shoots is greater when the cold, moist weather is per- 
sistent. It is, therefore, probable that the spread of the fungus 
throughout an infected leaf or shoot is directly assisted by the 
continuance of lessened vitality and water suffusion as growth 
progresses. 

Control. Preventive measures for the leaf curl have been made 
a subject of careful investigation throughout many years. It has 
finally been clearly shown that a thorough application of a fungi- 
cide, preferably Bordeaux mixture, during the late winter or early 
spring just prior to the opening of the buds, may prevent from 
90 to 95 per cent or more of the infections. I do not believe 
that subsequent sprayings are of any importance except in a case 
where the early spraying has been omitted ; and the fungus be- 
ing abundant, it is desired to cover up all parts of the plant with 
a spray so that the spores may be in large part killed as they are 
produced, or as budding is attempted. 



ASCOMYCETES 183 



III. PLUM rOCKETS 
E.xoascKs Pruiii Fuckel 



This fungus is the cause of the well-known deformities of 
the domestic plum, Priiiuis doincstica, and it is very generally 




P'lG. 67. Plum Pockets on Cultivated Prunus. (Photograph by 
H. II. Whetzel) 

distributed throughout Europe and portions of the United States. 
The etiolog)' and general life histoiy is not sufficiently different 
from the peach leaf curl to require detailed treatment, but the 



1 84 



FUNGOUS DISEASES OF PLANTS 



general characteristics of the abnormahties and special peculiarities 
of the fungus may be mentioned. The mycelium attacks the fruit 
buds and causes remarkable hypertrophies in the developing 
ovaries. The mesocarpic tissue is invaded, whereby it is stimu- 
lated to the production of an abundant spongy growth and the 
whole form of the plum is enlarged and distorted. Apparently the 
connection of the stone with its usual source of nutrition is broken 
up and no stone is developed, or else only a rudimentary structure. 
It is claimed that the mycelium is perennial, that here infection 
results by the growth of this mycelium into the young shoots and 




Fig. 68. Witches' Broom on Cherry, produced by Exoascus 
(Photograph by F. C. Stewart) 

ovaries in the spring. This point requires further investigation. 
As in the case of the peach leaf curl fungus, the ascogenous cells 
are developed beneath the cuticle and the elongating asci rupture 
the latter. The asci are densely crowded together and do not all 
mature at the same time. In general, the asci are 30-60 x 7-12 /u.. 
Robinson notes a certain dimorphism in the asci, slender ones 
measuring 43-60 x 5.5-7, and stout forms 27-35 X9-12/U,. In 
several instances I have attempted to inoculate young plums with 
spore-bearing material received from farther south, but such experi- 
ments have invariably failed. In general, a study of infection phe- 
nomena in the Exoascaceae would seem to be of much interest. 



ASCOMYCETES 1 85 

IV. WITCHES' BROOM OF THE CHERRY 
Exoijsciis Cerasi Fuckel 

This fungus is very common on both Prinuis avium and Pnni?is 
Ccrasus in luiropc. It has been reported only once in this country. 
The myceHum attacks tlie branches, and the stimulation due to its 
presence results in the formation of numerous twigs somewhat in 
the form of a loose broom (Fig. 68). According to some observers 
the twigs may be slightly thickened, although others claim that 
there is no abnormality in the latter. The leaves on affected twigs 
are also penetrated by the mycelium and they become somewhat 
reddish and wrinkled or crumpled. The asci develop upon the 
leaves, and measure, according to Sadebeck, 35-50 x 7-10/i (25- 
33 X 6-9 in specimens studied by Atkinson), During the fiowering 
period of PrumLs Cerastis the witches' brooms are very conspicuous, 
since the broom usually bears leaves only. 

Prevention in this case requires the destruction of all affected 
branches, as well, probably, as a thorough spraying about the time 
the asci are mature, and a subsequent one when the buds swell 
the following spring. 

Of the many other species of Exoascus the majority are para- 
sitic upon different species of Prunus, while Alnus, Populus, Acer, 
yEsculus, Carpinus, Crataegus, Pyrus, Ouercus, Ulmus, and other 
plants are also hosts. 

V. HELOTIACE.E 
The Helotiacese are Discomycetes of which the fruiting body is 
a distinct apothecium or cup. In texture these fungi may vary 
from wax-like to a rather tough consistency. The body is at first 
almost spherical and nearly or quite closed. With growth and dif- 
ferentiation it opens into the characteristic cup, sessile or supported 
by a stalk varying in length in different species. The sterile tissue 
of the cup is pseudoparenchymatous. The cylindrical asci arise 
from a hyphal-like hymenium, and each ascus contains eight spores. 
At maturity the ascus opens at the apex and forcibly ejects the 
spores, the latter being hyaline, diverse in form, and 1—8 celled. 
Filamentous paraphyses are present. Sclerotinia and Dasyscypha 
may be mentioned as containing parasitic species. 



1 86 FUNGOUS DISEASES OF PLANTS 

Of the twenty-five genera of this family, the genus Sclerotinia 
includes the most important parasitic species. It is characterized 
particularly by the fact that typically the fruit body arises from a 
sclerotium, which may be defined as a compact mass of hyphal ele- 
ments, sometimes distinctly pseudoparenchymatous or sclerotial in 
texture, serving commonly as a resting or more resistant mycelial 
stage. The sclerotium may be developed upon the living host or it 
may form after the death of the diseased structure. The apothe- 
cium is usually borne in this case on a rather long stalk, and it is 
smooth and more or less brown in color. The cylindrical asci 
bear in uniseriate fashion eight usually elliptical spores. Conidial 
and chlamydosporic stages may be present. 

VI. SCLEROTINIA 

De Bary, a. Ueber einige Sclerotinien und Sclerotinienkrankheiten. Bot. 

Zeitg. 44: 377-387 (et seq.). 1886. 
Wakker, J. H. Ueber die Infection der Nahrpflanzen durch parasitische 

Peziza- (Sclerotinia-) arten. Bot. Centrbl. 29 : 309-313,342-346. 1887. 
WORONIN, M. Ueber die Sclerotienkrankheiten der Vaccinieen-Beeren. Mem. 

de I'Acad. imp. de Sci. de St. Pe'tersbourg 36 (sen 8): 1888. 

Many species of Sclerotinia produce diseases of plants, and 
although several species have been carefully studied, there is 
much in the way of unconfirmed data. A monographic study 
of the genus is greatly needed. The apothecial or perfect stage 
is not developed, as a rule, until the mycelium, or a sclerotium, 
has undergone a period of rest. In several cases it is well estab- 
lished that the conidial stages are members of the form genus 
Monilia. It is also declared that other species include Botrytis 
forms in their life cycles. For convenience the following tentative 
classification of species of Sclerotinia is suggested : 

1. Species comprising in their life cycle not only apothecia, but also a 
Monilia stage, that is, with conidia produced in chains, the latter frequently 
separated one from another by special structural devices. 

a. Species in which both spore forms may be produced upon the same host ; 
such as Sclerotinia fn/ctigena, S. Vaccinii, S. Aiici/paricp, S. baccaru?)!., S. 
fuegalospora., and S. Oxycocci. 

b. Species whose life cycles are not complete upon a single host ; Stierotinia 
heteroica and .S'. Rhododciidri. 

2. Species which may embrace a form of Botrytis as a conidial stage; 
Sclerotinia Fuckeliana. 

3. Species in which no conidial stages have been convincingly demon- 
strated ; Sclerotinia Libert iana^ S. Bettthc, and 6'. TrifoUonnn. 



ASCOMYCETES 187 

VII. BROWN ROT OF STONE FRUITS 
Sch'/vti/iiii frmiigena (Pers.) Schroet.^ 

Aderhold, Run. Ueber eine vermuthliche zu Monilia fructigena Pers. ge- 

horige Sclerotinia. Ber. d. deut. hot. (ies. 22: 262-266. 1904. 
Humphrey, J. E. On Monilia fructigena. Bot. Gaz. 18 : 85-93. pi. y. 1893. 
Norton, J. B. S. Sclerotinia fructigena. Trans. Acad. Sci. of St. Louis 12 : 

91-97. pis. 18-21. 1902. 
QuAlNTANCE, A. L. The Brown Rot of Peaches, Plums, and Other Fruits. 

Ga. Agl. Exp. Sta. Built. 50: 237-269. Jigs, i-g, 1900. 
Smith, Erw. F. Peach Blight, Monilia fructigena., Pers. Journ. Myc. 5 : 

123-134. pls.s.,6. 
Sorauer, p. Erkrankungsfalle durch Monilia. Zeitsch. f. Pflanzenkr. 9 : 

225-235. //. 4. 1899. 
Wehmer, C. Monilia fructigena Pers. (= Sclerotinia fructigena m.) und die 

Monilia Krankheit der Obstbaume. Ber. der Deut. Bot. Ges. 16 : 298- 

307. pi. iS. 1898. 
WORONIN, M. Ueber Sclerotinia cinerea und Sclerotinia fructigena. M^m. 

de I'Acad. imp. d. Sci. de St. Petersbourg. VllP-Se'r. Phys.-Math. CI. 

10(5): I -38. pis. 1-6. 1899. 

The fungus causing the brown rot of fruits has been known 
botanically for half a century, but its great economic importance 
has only been appreciated during the past twenty years. It is now 
a well-known disease wherever the peach is grown throughout 
Europe and America. The conditions under which great injury 
results are, however, not general in all the countries named ; and 
therefore it may be very destructive one year and of relatively 
slight importance the following season. Whether warm or cool, 
moist weather is favorable to the spread of the disease, but the 
muggy weather of midsummer is particularly disastrous to the 
stone-fruit crop, on account of the rapid spread of the disease 
under such conditions. 

1 Under this title is discussed the widespread rot of stone fruits. Two species 
of Sclerotinia may, according to the work of Woronin, be distinguished as caus- 
ing somewhat different types of disease ; these species are Scle7vtinia fructigena 
and Sclerotinia cinerea. It is claimed that there are no observable differences in 
the mycelium of the two species, but that differences are evident in the color of 
the spore masses and in the susceptibility of hosts to the two forms. In Scle7v- 
tinia fructigena the spores are described as light brownish-yellow, or ochraceous, 
while in the other they are invariably gray. Moreover, in the former the spores 
are larger, averaging 20.9 X i2.\ii, while the latter average 12. i x 8.8/i. Scle/v- 
tinia cinerea is said to be most abundant on the common stone fruits, whereas 
Sclerotinia fructigena is also found on pomaceous fruits. The above view does 
not appear to be that generally held by American pathologists, and it is not uni- 
formly accepted in Europe. We shall, therefore, use the name Sclerotinia fructi- 
gena to designate this rot-disease of diverse stone fruits. 



1 88 FUNGOUS DISEASES OF PLANTS 

Extent of losses. The years when the greatest injury has been 
reported from various sections of this country are as follows : In 
1887 Dr. Erwin F. Smith reported it from Maryland and Delaware. 
The extent of the injury probably resulted in a shortage of the 
total crop estimated at 800,000 baskets of peaches. It was also 
very abundant in 1891 and 1893. Again, during subsequent years, 
it has been of considerable importance in the Delaware and Chesa- 
peake peninsula. In 1897 an almost total loss of the crop in 
Alabama was reported, the following year being somewhat less 
disastrous. Ouaintance states that the year 1900 was the worst in 
the history of commercial peach and plum growing in Georgia. 
He estimated the loss at 40 per cent of the total crop. This 
would mean a loss of between $500,000 and $700,000 for that 
state alone. 

Symptoms. The name brozvn rot has long been applied to this 
disease, and it is the one in most common use, although many 
others, particularly ripe rot, are also employed in some sections. 
This disease affects practically all stone fruits (Prunus spp.), very 
few varieties of either peach, apricot, nectarine, plum, or cherry 
be^ng free from it during seasons favorable to the fungus. The 
fruits are the most common seat of injury, but other vegetative parts 
are likewise susceptible. As a rule the fruits are apparently most 
easily attacked after they have become half grown, and the sus- 
ceptibility increases from this time to ripening. P'ruits in clusters, 
under which conditions moisture would be held, are more readily 
injured. 

The disease first makes itself evident as a small, dark brown, 
decayed spot. This spot increases in extent until the whole fruit 
is infested, but there is at first no diminution in size, and no sunken 
area develops. Before the whole fruit has become decayed, how- 
ever, evidences of a superficial development of the conidia of the 
fungus may appear. As a rule, however, the fungus develops its 
spores only after the fruit has decayed considerably. The fungus 
then breaks through the surface in the form of small tufts, con- 
sisting of masses of conidiophores with an abundant production 
of conidia, the appearance being as shown in Fig, 69. 

The flowers may also succumb, and that is more commonly 
the case the year after an unusual outbreak of the disease, due 



ASCOMYCETES 



189 




Fig. 69. Brown Rot of Plum : Monilia Stage 

generally to the fact that the old mummied fruits remaining on 
the twigs in large numbers serve to cause a very general infection 
at the time of blossoming. The twigs are also susceptible, but it has 
been quite definitely shown that infection of the twigs results only 



190 



FUNGOUS DISEASES OF PLANTS 



when either flowers or fruit produced on the twigs have already- 
fallen prey to the disease. In other words, the fungus must grow 
directly from the fruit or blossom into the young twigs, since it 
cannot readily penetrate the epidermis of the latter. Inoculation 

of the fungus into cuts on the 
bark will, however, also result in 
a twig infection. The effect of 
the fungus upon the twig is to 
produce a blight, the twig being 
completely killed as the disease 
progresses (Fig. 70). Peaches 
and apricots are more subject to 
the twig blight than other stone 
fruits. 

Mummied fruits. The fruit 
which has decayed may fall to 
the ground or hang upon the 
trees, gradually shrinking with 
evaporation each to a crumpled, 
dried mass, generally known as 
a mummy. These mummied 
fruits are the chief source of 
infection the following season 
under ordinary conditions. It 
has been determined that the 
spores produced one summer 
may, under certain conditions 
at least, live over until the fol- 
lowing spring. P'urther, the 
mycelium within the mummied 
fmits more readily lives until 
conditions favorable for growth 
the following season. It is also possible that the spores which 
have been blown about and adhere to bud scales, etc., may likewise 
cause infection the following year. 

Rot in market fruit. Not only is this fungus a cause of consid- 
erable loss in the orchard, but it also affects the fruit in shipment 
or on the market. When the spores are abundant in the orchard, 




Fig. 70. Ai'RrcoT Twig killed isy 
THE Brown Rot Fungus 



ASCOMYCETES 



191 



every fruit having perhaps some on its surface, these spores may 
germinate, under favorable conditions in transit, and cause infec- 
tion of the fruit in bulk, so that a shipment which showed great 
promise as it left the orchard may reach the market in practically 
worthless condition. 

Susceptibility of hosts. No very extensive data have been ac- 
cumulated with reference to the resistance or susceptibility of the 
many varieties of stone fruits in different sections of the country. 
In general, however, it 
would appear that among 
peaches the sorts densely 
covered with hairs or down, 
such as the Alexander, Hill's 
Chili, and Triumph, are un- 
usually susceptible. Among 
the more resistant sorts are 
to be found the Carman, 
Early Crawford, Elberta, 
Chinese Cling, and some 
others. Among the plums 
the Japanese varieties suffer 
generally in most sections 
of the country. The Amer- 
ican group of plums is also 
susceptible, and apparently 
more susceptible at the South than farther north. The Wild Goose 
and Marietta plums are much less affected in all regions. The 
native cherries are more resistant than such as the Montmorency. 

The fungus. The small tufts of the fungus, commonly called 
mold tufts, which appear on affected fruits and occasionally on 
blighted twigs are made up of conidiophores and the numerous 
conidia to which they give rise. The production of the aerial 
conidia usually indicates that the substratum is considerably pene- 
trated by the mycelium. This mycelium is light brown in color, 
rather closely septate, considerably branched, unequal in diameter, 
and somewhat nodulose or occasionally cellular in appearance. It 
is often vacuolate and may contain bodies differentiated as resting 
mycelial cells, or perhaps properly designated chlamydospores. 




Fig. 71. Section of Peach Twig affected 
WITH THE MoNiLiA. (After Erw. F. Smith) 



192 



FUNGOUS DISEASES OF PLANTS 



On blighted branches of the peach the mycehum has been 
found (Smith) to grow most abundantly in the cambium and soft 
bast, these tissues disappearing in large measure with the forma- 
tion of extensive gum pockets (Fig. 71). 

The conidiophores arise as short hyph^, which soon become 
septate at the extremities, branched and nodulose. The branching 
proceeds in an indefinite and usually irregular or semidichotomous 
fashion (Fig. 72, a and b). From the apex of these branches 
toward the base conidia are rapidly cut off, these cells remaining 
for a time simply moniliform or as branched chains, each con- 
striction between the nodulations eventually marking the line of 




Fig. 72. ScLFROTiNiA frvctigena: ConididI'Hores and Conidia, 
Section (jf Ai'otiiecium, Ascus, and Ascosi'ores 

separation between adjacent spores. The spores germinate readily, 
and often while still massed in the tuft of conidiophores, that is, 
before being blown or brushed away. Germination studies have 
shown that many of the conidia may live through until the suc- 
ceeding season, and, as indicated, the mycelium is even more 
capable of effective hibernation. 

Ordinarily no apothecial stage has been observed to intervene 
regularly in the life cycle of this fungus, and the ascosporous or 
Sclerotinia stage is not believed to be important to continue the 
propagation of the fungus. During the spring of 1902 the Scle- 
rotinia stage was found (Norton) quite commonly in the orchards 
of Maryland, The apothecia were discovered arising from scle- 
rotia, which might be developed either within the tissues or on 



ASCOMYCETES 1 93 

the surface of the mummied fruits. The fruits upon which this 
stage appeared had been hghtly covered with sandy soil for at 
least a year. In 1906 this stage was extremely common through- 
out the West. Conditions seemed to be most favorable for its de- 
velopment where the fruit had lain for eighteen months in little 
depressions in the sod, and fairly well covered by grass debris. 
The stalk or stipe of the apothecium was from .5 to 3 cm. in 
length, depending upon the distance of the mummy beneath the 
soil. The stipe is dark brown and the slightly bell-shaped disk 
is a shade lighter. The latter is usually 5-8 mm. in diameter, 
though it may range from 2 to 1 5 mm. The general appearance 




Fig. 73. Apothecia of Sclerotinia from Mummied Plums 

of the apothecia is shown in Fig. 73. The stipe consists of a 
medulla of elongated, intertwined, brown cells and a cortex of 
shorter, darker ones, the latter being continued in a tissue pro- 
jecting beyond the hymenium. The asci are cylindrical-clavate, 
125-215 X 7-10 /ti.i They arise from a dense layer of small 
hyphse, differing from the general medullary hyphae merely in be- 
ing more closely intertwined (Fig. 72, c and d). The ascospores 
are ellipsoidal and measure 10-15 x 5-8 /u.. They are obliquely 
uniseriate, or subseriate. The paraphyses are characteristic of 
many Pezizaceae, — hyaline, septate, simple or branched, filiform, 
and slightly swollen at the tips. 

1 Reade, J. M. Preliminary Notes on Some Species of Sclerotinia. Annales 
Mycologici 6 : 109-116. 190S. 



194 FUNGOUS DISEASES OF PLANTS 

Control. Preventive treatment should be begun in late winter 
or very early spring and must consider two possible sources 
of infection : (i) conidia adherent to bark or bud scales, and 
(2) the mummied, diseased fruits or blighted twigs. A thorough 
spraying, equivalent to disinfection with strong Bordeaux (6-6-50), 
would be effectual against the free conidia. In addition to such 
spraying, however (and it may be well to do this in late autumn), 
it is essential to destroy the old, diseased fruits. Prune them or 
knock them from their attachment to the twigs, rake them from 
beneath the trees, and destroy or turn under deeply. Spores may 
be blown long distances, however, so that an appearance of the 
disease may be expected at any time during the growing season, 
aside from the fact that it is hardly possible to kill all adherent 
conidia. In some sections of the country a 3—4—50 Bordeaux 
made with good lime has been used advantageously after foliage 
and fruit are well developed, with no injuiy resulting either to 
peaches or Japanese plums ; but this is not uniformly the case, 
and seasonal conditions unquestionably have a considerable in- 
fluence on the amount of injury caused by the spray. It might, 
where practicable, be employed until the fruits are more than 
half grown, after which time some other liquid spray or Bordeaux 
dust should be substituted. It is sometimes advisable to use a 
copper acetate solution (6 ounces to 50 gallons) when color be- 
gins to appear in the fruit. During a season of infrequent rains 
the writer has used a lime spray with some success. 

Some experiments have recently been made ^ with the lime- 
sulfur spray, and it is sufficiently promising to warrant trial. 
Apparently, the safest and most effective preparation is made 
by mixing i o pounds of sulfur and 1 5 pounds of good lime. 
Upon slaking the lime the sulfur is "self-cooked" from the 
heat generated, and the mixture is finally diluted to 50 gallons. 
During a single fairly dry season (a most favorable one for this 
mixture) the loss has been considerably reduced, — 73 per cent 
in the unsprayed plot as compared with from 10 to 30 per cent 
in the sprayed, 

1 Faurot, F. W. Brown Rot of Peach. Mo. State Hort. Soc. Rept. {1907): 
285-289. (Scott, who cooperated in this work, has also pubUshed the results of 
these experiments in detail. Compare Bureau Plant Ind., U. S. Dept. Agl. Circular 
1 : 12-16. 1908.) 



ASCOMYCETES Iqc 

Sclerotinia Vaccinii (Wor.) Rchm.^ This species occurs on 
shoots, leaves, and berries of the cowberry, Vaccinmm Vitis- 
idcea. In this fungus the chains of conidia show characteristic 
" disjunctors." The latter are fusiform cellulose structures sepa- 
rating the spores, and apparently important in dissemination. 
The conidial surface possesses an amygdaline aroma, by which 
insects are supposedly attracted. The diseased berries are yellow- 
brown when ripe. From sclerotia in mummied fruits which have 
lain on the ground over winter the apothecia are developed. The 
mature ascospores measure 14-17 X 7-9 ft. 

Sclerotinia Aucupariae Ledw.^ has been found in Finland and 
in Germany on the leaves and fruit of Pirns Aitcitparia. 

Sclerotinia baccarum Schroet.^ is the cause of the sclerotial 
disease of the bilberry, Vacciiiiujn Myrtillus. In this species the 
apothecia are relatively large and stout, measuring 5-10 mm. in 
diameter, with stalks often 5 cm. in length. The spores are. 
18-20 X 9/U-. 

Sclerotinia megalospora Wor.,^ on the berries and leaves of the 
crowberry, Enipctnini nigrum, has large, more nearly spherical 
conidia than those above described, and the ascospores, invested 
with a distinct gelatinous envelope, measure 20-25 X 14-16//.. 

Sclerotinia Oxycocci Wor.^ produces the sclerotial disease of the 
cranberry, Vaccininm Oxycoccns. This species is morphologically 
and physiologically interesting on account of the difference in 
size of the spores, four being large and capable of germination, 
while the other four are considered to be ill developed and in- 
capable of germination. This suggests an interesting differentia- 
tion of the nuclei. Even the larger spores are relatively small for 
this group, measuring 12-14 X 6-7/i. 

Sclerotinia heteroica Wor. & Nawasch.^ According to Woronin 
this species produces upon Vaccininm nliginosnm a conidial stage, 
which conidia are able successfully to infest the ovaries of Lcdnm 
palustrc, but no conidia are produced on Ledum. On the latter 
host, however, the sclerotial stage is developed. This fungus 

1 Woronin. Ueber die Sclerotienkrankheiten d. Vaccinieen-Beeren, /. c. 

2 Woronin. Ber. d. deut. bot. Ges. 9 : 102-103. 

3 Woronin. Ueber die Sclerotienltrankheiten d. Vaccinieen-Beeren, I.e. 
*Nawaschin. Ber. d. deut. bot. Ges. 12 : 117-119. 



196 FUNGOUS DISEASES OF PLANTS 

apparently requires two hosts to complete its development and is, 
therefore, an instance of what is denoted heteroecism, a condition 
discussed more at length under the rust fungi. 

Sclerotinia Rhododendri Fischer, ^ like the preceding, appears 
to be heteroecious in character. It is found on Rhododendron 
fcmigincnm and Rliododcndron Jiirsutinii. 

VIII. GRAY MOLD, OR BOTRYTIS DISEASE 
Sclerotinia Fiickclia)ia I)e Bary 

Brooks, F. T. Observations on the Biology of Botrytis cinerea. Ann. Bot. 

22: 479-484. , figs. 1-4. 1 90S. 
IsTVANFFi, G. DE. Etucles microbiologiques et mycologiques sur le rot gris de 

la vigne. Ann. d. I'institut central ampel. roy. Hongrois (1905): 183-360. 
KissLiNG, E. Zur Biologie der Botrytis cinerea. Hedwigia 28 : 227-256. 

1889. 
NoRDHAUSEN, M. Beitrage zur Biologie parasitaren Pilze. Jahrb. f. wiss. 

Bot. 33: 1-46. 1898. 
Smith, R. E. Botrytis and Sclerotinia. Botan. Gaz. 29 : 369-407. ph. 25- 

27. figs. 1-3. 1900. 
Smith, R. E. The Parasitism of Botrytis cinerea. Botan. Gaz. 38: 421-436. 

1902. 

Occurrence and effects. In the conidial stage this is one of the 
most common fungi known upon vegetation. It may propagate 
itself indefinitely as a saprophyte upon fallen or dejected flowers 
and leaves, or upon decaying organic matter. Again, it may, as 
a parasite, produce a variety of rots, decays, or stem diseases, 
especially in greenhouse or other plants grown under moist, 
warm conditions. 

In Europe it is important as a disease of the leaves and fruit 
of the grape. While such injuries may be serious, the abundance 
of this fungus on the fruit, in certain regions, late in the season 
gives promise of high-class wine production. The grapes are then 
juicy and rich in sugar. It attacks other woody plants. Smith re- 
gards the Botrytis Dojiglasii Tubeuf,^ reported destructive to 
young conifers, as synonymous with this species, and he has 
found it responsible for a disease of the linden {Tilia par^oiflord) 
in the nursery. It seems to be the less frequent cause of lettuce 
" drop " in the greenhouse. This disease, subsequently discussed 

1 Fischer. Ber. d. schweiz. bot. Ges. 1894. 

2 Tubeuf, K. von. Botan. Centrbl. 33 : 347. 1888. 



ASCOMVCETES 



197 



more at length, may begin and develop in various ways when 
Botrytis is the cause, but it is finally known by the complete 
collapse of the lettuce heads due to the death of the stem and leaf 
bases. The conidial stage is also associated with various damping-off 
diseases, and it is believed by Smith to be the organism studied by 
Marshall Ward as the cause of an important lily disease. ^ In all 
cases the conidial stage of the fungus may develop abundantly 
upon the dead parts, and it has the appearance of a gray mold. 





Fig. 74. BoTRVT/s c/nerea. (After R. E. Smith) 
a, portion of conidiophore ; l>, organ of attachment 

The fungus : morphology and biology. Under Sclerotinia 
Fuckelimia it is intended to include the forms of disease which 
may be attributed in Europe to Bottytis cincrca Pers. and in 
America to Botrytis vjilgaris Fr. It has been satisfactorily dem- 
onstrated that these two names apply to a single species, a typical 
conidiophore of which is illustrated in Fig. 74. The observations 
of De Bary first connected this conidial stage with an apothecial 
form, Sclerotinia Fnckeliana, produced from sclerotia of the Bo- 
trytis on grape. Subsequently doubt arose regarding this connec- 
tion, since many observers failed repeatedly to secure under any 

1 Ward, H. Marshall. Ann. Bot. 2 : 319-382. ph. 20-24. 1 888. 



198 



FUNGOUS DISEASES OF PLANTS 



conditions the perfect form from sclerotia of the Botrytis. It would 
seem that Istvanffi has now secured substantial proof that these 
are pleomorphic stages of a single fungus. 

Much interesting biological work has been done upon this 
fungus. Infection results most readily from sclerotia or from 
a mycelium which has been growing saprophytically. Infection 
frequently fails when conidia germinate directly upon the sur- 
faces of delicate parts. Upon penetrating a plant there is, first, 
a direct poisoning effect, supposedly due to oxalic acid, resulting 
in the death of adjacent cells ; and, second, there is more or less 
digestion of the cell contents and membranes. 




Fig. 75. ScLEROTiNfA LiBERTiANA. (After R. E. Smith) 
(7, sclerotia and apothecium ; b, penetration of hyphae 

Control. In the case of this fungus, as well as the species of 
Sclerotinia next discussed, good sanitation is important. Never- 
theless, in the greenhouse it may be necessary to sterilize the 
soil in order to control the disease effectively when it becomes 

virulent. 

IX. LETTUCE DROP 

Sclerotinia Libertiana Fuckel 

Humphrey, J. E. Diseases of the Cucumber Plant. A Sclerotium Disease. 
Mass. Agl. Exp. Sta. Rept. 10: 212-224. pl^- J-^- 1892. 

Smith, R. E. Botrytis and Sclerotinia : Their Relation to Certain Plant Dis- 
eases and to Each Other. Bot. Gaz. 29 : 369-407. ph. 2^-2y. 

Stone, G. E., and Smith, R. E. " Drop " of Lettuce. Mass. (Hatch) Exp. 
Sta. Rept. 9: 79-81. 1897. (Compare, also, 10 : 55-58, 1898; and 11 : 
149-15 1, 1899.) 



ASCOMYCETES 1 99 

Symptoms, effects, and hosts. It is difficult to determine how 
many of the reported sclerotial diseases of greenhouse and garden 
crops may be due to this fungus. It is unquestionably, however, 
one of the most disastrous of the sclerotium-producing fungi, and 
it is, moreover, widely distributed and not readily controlled. So 
far as can be judged from the studies and experiments which 
have been made, it is the cause of the worst type of the lettuce 
"drop," a disease of great importance in the greenhouses of the 
eastern states. 

As this disease commonly occurs there is little or no evidence 
of the incipient stages in the form of definite spots or ulcers. 
The host plants may show some evidences of flagging, in a short 
time there are indications of water-soaked areas over the stem 
and basal portions of leaves, and finally the whole plant collapses 
and melts into a formless mass. 

Even from early evidences of the disease fungus threads may 
appear upon the surface of the leaf, and this mycelium may be- 
come superficially conspicuous, even resulting in the development 
of small sclerotia. These appear first as white specks and later 
take the form of deep black, rather irregular sclerotia, as shown 
in Fig. 75, a. This fungus quickly spreads from plant to plant 
through the soil, and furthermore, in its relation to healthy 
plants, results almost invariably in the production of the disease. 
De Bary showed that ascospores are commonly ineffective in pro- 
ducing direct infection, but sclerotia or bits of the mycelium may 
serve for inoculation purposes. The Sclerotinia Libcrtiaiia type 
of sclerotium will yield almost invariably the apothecia of the 
Sclerotinia. 

This fungus is apparently widespread. It has been reported by 
various observers as a cause of destructive diseases of hemp, rape, 
cucumbers, and of many forced vegetables and bulbous plants. A 
disease of the tobacco, discussed by Clir^ton,^ has also been attrib- 
uted to this fungus. 

The life cycle. In no case has it been possible positively to iden- 
tify a conidial stage in the life cycle of this species, although Botrytis 
cincrca has frequently been found upon plants unquestionably 

1 Clinton, G. P. Tobacco Diseases. Stem Rot. Conn. Agl. Exp. Sta. Rept. 
(1906) : 326-329. pis. 20 a, b ; 21 a. 



200 FUNGOUS DISEASES OF PLANTS 

affected with this sclerotial disease. From a series of experi- 
ments extending through several years, Smith was unable by 
any means to produce a conidial stage from cultures of the 
Sclcrotitiia Libcrtiana sclerotia, and he believes, moreover, that 
there exists another type of this fungus in which no conidia are 
produced and in which the more minute sclerotia are incapable 
of producing the apothecia. Whether or not there is any connec- 
tion between the large sclerotinial type, which must be designated 
as Sclcrotinia Libcrtiana, and the smaller type above referred to, 
it is unquestionably true that there exists a disease of lettuce and 
other greenhouse plants of which the small sclerotium-producing 




Fig. 76. The Lettuck Dkui-: Control (Healthy) and Inoculated 
(Diseased) Plants 

fungus is the cause. The writer has found this type of the fungus 
to be the cause of an important disease of lettuce in New York 
and Boston, and inoculation experiments have invariably shown 
the disease to be unusually virulent (Fig. 76). Sclcrotinia Liber- 
tiana has been several times reported as an important disease of 
the cucumber, and according to Humphrey it is rather common 
in the cucumber houses in Massachusetts. Piumphrey supposed, 
however, that the Botrytis which he found upon diseased plants 
was connected with the sclerotial stage, but no sufficient proof of 
such connection is afforded by the work which he reports. 

The sclerotia of this species are said to reach 3 cm. in length 
in exceptional cases. The asci are cylindrical, and measure 130- 
135 X 8-io/x., while the spores are small, — 9-13 X 4-6.5 ix. 



ASCOMYCETES 20I 

X. STEM ROT OF CLOVER 

Sclerotinia Trifoliorum Eriks. 

Chester, F. I). Rot of the Scarlet Clover. Del. Agl. Exp. Sta. Rept. 3 : 

84-88. 1890. 
Eriksson, J. Bot. Centrbl. 1 : 296. 

This fungus is occasionally very destructive to various species 
of clover (Trifolium) in Europe, and it has several times been 
reported as epidemic in the United States. In this country, how- 
ever, it is not so widely distributed or so constant in its injurious 
effects as to have been often observed. The effect of this fungus 
upon the host is to produce a decay near the base of the stool, or 
practically at the surface of the ground, as the result of which the 
plant wilts. The mycelium, which is from the beginning evident 
on the surface, invades the tissues and ordinarily by the time that 
the plant is killed numerous small, black sclerotia are produced 
upon the surface of the affected parts. The sclerotia vary in size 
from I to 5 or 6 mm. in diameter. Sown upon moist sand or 
wintered upon the decaying remains of the host there are pro- 
duced the following spring the brown apothecia characteristic of 
this species. The asci are long cylindrical, about 180 x 12 /a. 
Ascospores, which are disseminated in the early spring, lose 
their power of germination upon being dried, and it would seem, 
therefore, that they must penetrate the host at this time. It is 
claimed, on the other hand, that the sclerotia may retain their 
vitality for a period of several years if the conditions are un- 
favorable for germination. Some regard this fungus as identical 
with Sclerotinia Libertiaita. 

Sclerotinia Betulae Wor.^ This birch catkin disease is common 
in birch forests of Russia. Sclerotia, so far as is known, are pro- 
duced during the development of the catkins, falling and remain- 
ing on the ground over winter. The apothecia are formed the 
following spring, each sclerotium producing several small apo- 
thecia of light color. The fungus has also been found in Europe, 
Asia, and America. 

Sclerotinia tuberosa (Hedw.) Fckl. develops enormous sclerotia 
on the rhizomes of Anemone neniorosa. 

^ Tubeuf. Diseases of Plants, /. c, 261. 



202 FUNGOUS DISEASES OF PLANTS 

XI. LARCH CANKER 

Dasyscypha WiUkcrmmii Hartig. 

Haktig, R. Die Larchenkrankheiten, insbesondere der Larchenkrebspilz. 
Untersuch. aus d. Forstbotan. Institut Miinchen 1 : 63-87. 1880. 

Occurrence and effects. The larch canker is one of the most 
important diseases of this host in certain districts of Europe. It 
is particularly abundant in the moist, marshy, mountain meadows, 
but is seldom of importance on hillsides or slopes. The fungus 
is a typical canker-producing organism, and, so far as is known, it 
gains entrance to the host only through wounds. It spreads most 
rapidly in the phloem elements and rapidly causes the death of 
the bark. The diseased areas become shrunken and brown. The 
bark may peel away in places and pronounced cankers develop. 
The fungus appears to spread rapidly only during seasons when 
the host plant is comparatively inactive, as during the autumn 
and winter. The wounds of the previous year may, therefore, 
be practically healed over during the growing season, but the 
following autumn the fungus continues its spread, and in time 
large limbs or trunks may be completely girdled and death result. 
The needles on affected twigs begin to show the presence of the 
fungus during the late summer. 

The fungus. Upon the death of the bark the fungus appears 
superficially in the form of creamy or yellowish-white stromatic 
tufts. Upon the minute conidiophores there are produced simple 
hyaline conidia. The latter have not been germinated and do not 
appear to be important in the immediate distribution of the fungus. 
Later in the season the apothecia may appear on the diseased areas 
if there is sufficient moisture. The apothecia are short stalked, 
almost sessile, yellowish without, and orange colored within. The 
asci measure about 1 20 x 9 /a. They are cylindrical in form and 
contain invariably eight ovoidal, unicellular spores. Between the 
asci are interspersed a considerable number of filiform paraphyses. 
Inoculation experiments have demonstrated that this fungus is the 
cause of the canker with which it is associated. No preventive 
measures can be recommended when the fungus is once estab- 
lished on larch plantations, and, therefore, in locating new planta- 
tions, one should bear in mind the conditions under which the 
fungus is most disastrous. 



ASCOMYCETES 



203 



XII. MOLLISIACE^ 

This family differs from the Helotiaceae largely in texture, the 
former being tougher, and as a rule made up of hyphal cells 
modified in a prosenchymatic or fibrous manner. The spores are 
hyaline and very similar to those of the Helotiaceae. The only 
genus of importance in producing plant diseases is Pseudopeziza. 




Fig. 77 rt. Alfalfa Leaf Spot. (Photograph by H. H. Whetzel) 

Pseudopeziza. In this genus the apothecium is formed beneath 
the epidermis, which is later ruptured, and the mature fruit body 
is relatively simple in structure and shallow. The asci contain eight 
unicellular spores. 

XIII. ALFALFA LEAF SPOT 

Pseudopeziza Medicagiiiis (Lib.) Sacc. 

Combs, Robt. The Alfalfa Leaf Spot Disease. Iowa Agl. Exp. Sta. Built. 
36: 858-859. 

The alfalfa leaf spot is often very abundant both in Europe 
and America, and particularly injurious during rather dry seasons. 



204 



FUNGOUS DISEASES OF PLANTS 




Fig. 77 b. Alfalfa defoliated by 
THE Leaf Spot Fungus. (Photo- 
graph by H. H. Whetzel) 



Small sooty brown or black spots 
about -,V inch in diameter are 

1 D 

produced, first evident on the 
upper surfaces of the leaves (Fig. 
78). In these spots there appear 
later in the season the relatively 
simple, sessile apothecia, which 
are formed beneath the epidermis 
and break through at maturity. 
The spots are often very numer- 
ous, causing defoliation of many 
of the leaves by the latter part 
of summer. These structures are 
saucer-shaped, flat, and light in 
color, at first fleshy in texture. 
The club-shaped asci bear eight 
unicellular colorless spores in 
two series, measuring i o- 1 4 /u. in 
length. Paraphyses are also pres- 
ent. The mycelium is very local 
and confined to the area of the 
spots. This fungus is very closely 
related to the species causing a 
leaf spot of clover, Pseudopcziza 
Trifolii, and with this species it 
may be identical. No practical 
method of controlling this dis- 
ease has been developed. 



XIV. ANTHRACNOSE OF CURRANTS 



Psendopeziza Kibis Kleb. 

Dudley, W. R. Anthracnose of Currants. Cornell Agl. Exp. Sta. Built. 15 : 

196-198. 1889. 
Klebahn, H. Untersuchungen iiber einige Fungi imperfect! und die zuge- 

horigen Ascomycetemforem. Ill Gloeosporium Ribis (Lib.) Mont, and 

Desm. Zeitsch. f. Pflanzenkr. 16: 65-83. ph. 3-4. 1906. 
Stewart, F. C. An Epidemic of Currant Anthracnose. N. Y. (Geneva) Agl. 

Exp. Sta. Built. 199: 64-80. 1901. 



ASCOMYCETES 



205 



Distribution and occurrence. This anthracnose is a disease well 
known in Europe and America. Periodically since 1 884 it has been 
mentioned as a destructive fungus to both white and red currants 
in New York. The fungus 
has also been found upon 
black currants and goose- 
berries, but it has never, 
apparently, amounted to an 
epidemic. Among red cur- 
rants Stewart observed that 
Prince Albert and President 
Wilder were practically free 
from injury where Fay's 
Prolific and Victoria were 
seriously affected. 

Affected leaves are more 
or less covered with small 
brown spots, as shown in 
Fig. 158. When the trouble 
is serious the leaves turn 




wdDowMoDooaoOi 



Fig. 78. PsEUDOPEZizA Medicaginis : 
Structural Features. (After Comes) 



yellow and drop. The fun- 
gus also occurs on petioles, 
young canes, fruit stalks, and fruits. It is believed that it may 
pass the winter on the canes. 

The fungus. Until 1906 this fungus was known by an im- 
perfect stage alone, which like that of the bitter rot of the apple 
subsequently discussed was referred to the genus Gloeosporium, 
and bore the name Ghvosporijtm Ribis. The Gloeosporial stage 
(cf. Gloeosporium) is in fact the only stage of the fungus which is 
produced upon the growing plant. The pustules or acervuli con- 
sist of a stromatic portion from which arise numerous conidiophores, 
bearing elliptical or strongly curved, falcate conidia. These fruit- 
ing masses rupture the epidermis and the spores escape in a gelat- 
inous mass. The acervuli are produced very abundantly on both 
surfaces of the leaves but particularly upon the upper surfaces. 
The spores are commonly 1 9 X 7 /a, varying, however, from 1 2- 
24 X 5-9 At. Formerly, it was suggested that this gloeosporial form 
might be connected with Gnomoniella circinata (Fckl.) Sacc. 



206 



FUNGOUS DISEASES OF PLANTS 



Klebahn in his investigations of this fungus ascertained that 
when the leaves are wintered over under suitable conditions of 
moisture an ascigerous stage is developed the following spring. 
This stage proved to be a Pseudopeziza ; that is to say, a 
Pseudopeziza was one of the most abundant of the perithecial 
stages found on wintered leaves. The spores of other perithecial 
forms yielded upon inoculation of the growing leaves no result, 
whereas spores of the Pseudopeziza developed in due course of 











Fig. 79. Anthracnose on Currant Leak. (Photograph by 
F. C. Stewart) 

time the Gloeosporial stage upon growing parts. The ascigerous 
stage develops as a small fungous body of rapidly growing tissue, 
completely immersed in the leaf, and more or less surrounded by 
the old hyphae of the Gloeosporial form. With further develop- 
ment the epidermis is ruptured and the apothecium opens as a 
fleshy disk-shaped structure, the basal portions of which consist 
of more or less pseudoparenchymatous tissue from which arise 
numerous asci and paraphyses. The basal portion remains in 
part surrounded by thick-walled cells of the old mycelium, as 



ASCOMYCETES 



207 



shown in Fig. 80, b. The asci are club-shaped and bear eight 
hyahne ovoidal spores. The paraphyses are simple or branched, 
sometimes once-septate and slightly club-shaped. 

This fungus shows in pure culture certain growth characteristics 
which seem to differentiate it somewhat sharply from other species 
of Gloeosporium. In the first place it grows slowly upon nutrient 
agar, several months being required to produce a colony of several 
millimeters in extent. The hyphae become considerably colored 




^^^^ 




W" 

^ ^ 



Fig. 80. PsEVDOPEzizA Km is. (h, after Klebahn) 
a, conidial stage ; A, section of apothecium 

and often gray- green in appearance. The central portion of the 
colony gradually forms a stromatic body. The cultures of the 
ascus stage yielded the same type of colony, which is further 
proof of the genetic connection between the two spore stages. 
This is the first time that a fungus with all the characteristics 
of a Gloeosporium has been experimentally connected with an 
ascigerous form belonging to the Discomycetes. 



XV. PHACIDIACEvC 



In this family the apothecium develops with a surrounding 
stroma, which is ordinarily coherent with the substratum. At 



208 



FUNGOUS DISEASES OF PLANTS 



the outset the apothecium is closed, but opens by a circular or 
transverse split, and the edges are often torn or bent back as 
distinct lips or lobes. The apothecia are usually tough and 
leathery. The asci and paraphyses form a very closely adherent 
layer, in which the paraphyses overlap above the summit of 
the asci, forming a rather definite epithecium. Rhytisma is the 
only genus which is here of importance. 



XVI. THE BLACK SPOT OF MAPLE 
Rhytisma Accrimim (Pers.) Yx. 

Klebahn, H. Bemerkungen iiber KJiyfisina acerinuni und liber die Arbeit 
des Herrn. Dr. Julius Miiller iiber die Runzelschorfe. Bot. Centrbl. 58: 
321-323. 1894. 

MiJLLER, J. Zur Kenntniss des Runzelschorfes und der ihm ahnlichen Pilze 
Jahrb. f. wiss. Botanik 25: 607-627. ph. 2'/-2g. 1893. 

The black spot of the maple (Acer spp.) is a fungus of very 
wide distribution, but the amount of injury caused is so slight 
that it cannot be considered of much economic importance. The 

affected areas of the leaf are so 
conspicuous, however, as to attract 
the attention of all interested in 
parasitic fungi (Fig. 81). The 
fungus occurs upon a number of 
species of Acer, the first evidences 
of the spot being manifest by yel- 
low, thickened areas soon after the 
leaves have attained full size. A 
cross section shows that beneath 
the cuticle there are produced in 
great quantity on short conidio- 
phores arising from a stromatic tissue unicellular, curved conidia, 
and these conidia serve to spread the fungus, it is believed, during 
the same season. This stage is referred to the form genus Melas- 
mia. The tough blackened structures, which appear in the affected 
spots as the season advances, consist in reality of sclerotioidal 
masses of fungous tissue, black without but white within, penetrat- 
ing all medullary parts of the leaf. These areas are much thicker 
than the normal leaf. After the fall of the leaf further growth or 




Fic,. 81. The Black Spot of Maple 



ASCOMYCETES 209 

differentiation takes place in the sclerotial areas, so that there is 
finally developed by the next spring rather unlimited, complex 
apothecia, often 1.5 cm. broad, which rupture by irregular fissures 
along the ridges of the wrinkled surface. The asci are club-shaped, 
and bear eight needle-shaped spores. Numerous paraphyses with 
incurved or hooked tips are present. The asci are 120—130 X 9— 
10 fjL. At maturity the large spores (65-80 x 1.5-3 At) are ejected 
forcibly from the ascus, doubtless distributed by the wind, and 
they are provided with a mucilaginous membrane which, accord- 
ing to Klebahn, serves for adherence to the host. Artificial infec- 
tion with ascospores has been effected, and after such infection 
the pycnidial stage may be produced within about eight weeks. 

Among other common and conspicuous species of Rhytisma 
of wide distribution are Rhytisma Salicinum (Pers.) Fr. occur- 
ring on various species of Salix ; Rhytisma Vaccinii (Schw.) Fr. 
on species of Ericaceae, notably Vacciniiim arborcnm in the 
Appalachians. 

XVII. PERISPORIALES 

This order includes a few families well distinguished from the 
preceding Ascomycetes by the presence of a more or less mem- 
branous, generally spherical, closed fruit body, or perithecium, 
produced directly on the mycelium. In the two families which may 
here be considered, Perisporiaceae and Erysiphaceae, there is no 
mouth or ostiolum. The families may be distinguished as follows : 

Perisporiaceae. Mycelium generally dark in color ; perithecium 
without differentiated appendages, and conidial stages not com- 
parable to the form genus Oidium. 

Erysiphaceae. Mycelium generally hyaline ; perithecium with 
appendages, often highly modified ; and conidial stage, when 
present, invariably an Oidium. 

XVIII. PERISPORIACEAE 1 

This is a small family although some authors may include 
in it as many as twenty genera. The genera, as a rule, comprise 

^ The two genera which are here discussed have been included by Fischer 
(Engler and Prantl, /. c.) in the Plectascineas, and there is considerable diversity 
of opinion as to their true position. 



2IO FUNGOUS DISEASES OF PLANTS 

very few species. Some are parasitic and some saprophytic, 
some with superficial mycelium, and others with mycelium pene- 
trating the substratum. Two genera which are important in this 
connection are Thielavia and Meliola. In the former genus the 
Mycelium is immersed in the host. The perithecia are mem- 
branous, without appendages, and subsidiary fruit forms include a 
stage with endogenous spores. In the genus Meliola, the mycelium 
is superficial and brown. The perithecia are beset with simple oi 
branched appendages. The spores are brown and two-celled. 

XIX. ROOT ROT OF TOBACCO, VIOLETS, PEAS, LUPINES, ETC. 
Thielavia basicola (B. & Br.) Zopf. 

Briggs, L. J. The Field Treatment of Tobacco Root-Rot. Bur. Plant Ind., 

U. S. Dept. Agl. Circular 7: i-8. 1908. 
Clinton, G. P. Root Rot of Tobacco. Conn. Agl. Exp. Sta. Rept. (1906): 

342-368. pis. 2g-32. 
Thaxter, Roland. Fungus in Violet Roots. Conn. Agl. Exp. Sta. Rept. 

(1891): 166-167. 
ZoPF, W. Ueber die Wurzelbraune der Lupinen, eine neue Pilzkrankheit. 

Zeitsch. f. Pflanzenkr. 1: 72-76. Jigs, i., 2. 1891. 

This fungus, which is now known to cause in the United 
States, under certain climatic and soil conditions, a serious 
disease of tobacco {Nicotiana Tabacum), was first studied in 
Europe as a parasite of less consequence upon peas, lupines, etc. 
The morphology of the fungus and its relation to a disease of 
Scjiccio elegatis was established in 1876. The fungus was found 
in the United States on violets {Viola odorata) in 1891, and sub- 
sequently on other plants ; but in 1 906 it was recognized in 
Connecticut as an important tobacco parasite. 

Distribution. Upon one or more of its hosts the fungus has 
been found, in general, from Ohio eastward in the United States, 
and in western Europe from England to Italy. The fungus has 
not been reported from the southern states growing tobacco, 
or from tropical regions. It is believed that abundant moisture 
is essential for serious trouble by this fungus, lack of drainage 
and other factors assisting in producing this condition. Briggs 
has recently shown that the presence of this fungus in tobacco 
soils is an indication of alkalinity, a condition often brought 
about by the system of fertilization. 



n 



ASCOMYCETES 



21 I 



Host Plants. The following is a list of the natural hosts, as 
compiled by Clinton: Ginseng, Ai-alia quinqncfolia ; Begonia 
rubra; Brgojim sp.; horse radish, CocJdcaria Armoracia ; Cycla- 
men sp. ; lupines, Liipinns albus, Liipinus angjistifo litis, Lnpinus 
lutens, and Liipinus therviis ; Nemophila anric?tlata ; tobacco, 
Nicotiana Tabacuni ; Onobrychis Cristagalli ; pea, Pisnni sa- 
tivum ; Trigonella ccerulca ; and violet, Viola odorata. It is 
therefore evident that a variety of dicotyledonous plants may 




Fig. 82. The Thielavia- Disease of Tobacco. (After G. P. Clinton) 
Healthy and diseased root systems 

be attacked. The leguminous hosts are, however, most numerous, 
and the fungus is quite frequent on garden and sweet peas. 

Pathological effects. Roots affected by the Thielavia do not 
develop a normal root system, or they may be injured to such 
an extent that on pulling up an affected plant from a moist soil 
practically everything except a stub of a root will be broken off. 
In the case of the tobacco a cluster of new roots may form on 
the crown above the first injuries (Fig. 82). The fungus is ap- 
parently most injurious in the seed beds. Affected plants may 
not be killed, and many go through the season with a stunted 
growth, or with such a check upon vigorous development at the 



212 



FUNGOUS DISEASES OF PLANTS 



outset as to cause manifest loss in the final crop. Again, diseased 
plants may entirely recover. 

The surfaces of diseased roots may be roughened and browned 
by the presence of the fungus, but the tissues within are usually, 
in the case of violets, peas, etc., tinted red or pink. Ordinarily 
the fungus penetrates all parts of the rootlet, but as is common 
with plants which are not vigorous or obligate parasites, there are 
no abnormal cell divisions of the host. 

Morphology of the fungus. The mycelium is intercellular, 
abundantly septate, and at first hyaline. The threads are narrow, 

and the branches are cut off by a 
septum at a slight distance from 
the main hypha, somewhat as in 
Rhizoctonia {Corticunn vagmn). 
Three kinds of spores have 
been commonly found, namely, 
(i) endosporous conidia; (2) thick- 
walled conidia, or chlamydo- 
spores ; and (3) ascospores. 

I. The endospores are an 
interesting type of spores formed 
in chains in terminal branches or 
clusters of branches (Fig. 83, «). 
These spores are formed by basi- 
petal septation as short cylindrical 

cells within the branch. The tip 
Fig. 83. Conidia AND Chlamydo- ^^ ^j^^ ^^^^^^ -^ ^^^j, ^^^^^^ 

SPORES OF THIELAVIA "' 

and they are pushed out by os- 
motic force, the branch assuming the part of a spore case. The 
endospores are distinctly hyaline, and as produced in artificial cul- 
tures, they may remain united in short threads, or cohere laterally 
as small rafts. Individuals measure about 10-20 x 4-5 /*. 

2. The chlamydospores are thick walled, more or less cy- 
lindrical, brown spores, borne in chains, the early stages of for- 
mation differing apparently only in size from the endospores. 
At maturity, however, the short chains, or rather the colored 
spore cells of these, break up, as shown in Fig. 83, ^, measuring 
about 1 2 /A in width. 




ASCOMYCETES 2 1 3 

3. The perithecia bcarinp^ the ascospores are relatively simple. 
The asci are evanescent, and the spores unicellular, lenticular, 
vacuolate, and measure about 1 2 x 5 /a. 

Artificial cultures are readily made on various media, and 
the first two spore stages may be quickly produced in culture, 
the endospores, particularly, being aerial. The association of the 
ascosporous stage with the others and the apparent continuity 
of mycelium are believed to show genetic connection. 

Control. Since the seed bed is perhaps the greater source 
of trouble in the case of tobacco, sterilization of the soil where 
the disease has become established may be necessary. Diseased 
plants should not be used for planting. Thorough aeration of 
the soil by drainage and cultivation is also desirable. The sug- 
gestion that this fungus is constantly associated with an alkaline 
soil requires an investigation of the soil conditions with a view to 
correcting this by subsequent fertilization. 

XX. SOOTY MOLD OF ORANGE 

Meliola Camellice (Catt.) Sacc. 

Farlow, W. G. On a Disease of Olive and Orange Trees, occurring in Cali- 
fornia in the Spring and Summer of 1895. Built, of the Bussey Institu- 
tion 5 : 404-414. 1876. 

Webber, H. J. Sooty Mold of the Orange and Its Treatment. Div. Veg. 
Phys. and Path., U. S. Dept. Agl. Built. 13: 1-34. pis. i-j. 1897. 

Distribution and effects. The sooty mold is a disease which is 
probably distributed throughout all moist citrus-growing regions. 
It is perhaps most injurious upon the orange, but it occurs also 
upon the other cultivated citrous fruits. In one sense it is scarcely 
to be regarded as a fungous disease, since the fungus which pro- 
duces the obnoxious effect is probably not parasitic. Nevertheless, 
the fruit infested by the sooty mold is seriously injured from the 
commercial standpoint, and since it is the fungus which effects 
this injury, it may justly be considered in this connection. 

The sooty mold consists, as the name implies, of a sooty 
growth, or crust, which occurs both upon leaves and fruit. It 
may appear in isolated patches or investing practically the entire 
leaf or fruit surface. The black mass is made up entirely of 
fungous hyphae. The fungus is only found following the attack 



2 14 FUNGOUS DISEASES OF PLANTS 

of certain scale insects. In Florida it commonly succeeds attacks 
by the white fly, or Aleyrodes. It is, however, in other localities 
equally as abundant following other species of aphid-like insects. 
The fungus has long been a nuisance in the Mediterranean 
orange groves, and for some years has been of sufficient abun- 
dance in both Florida and California to require control measures. 

The fungus. The mycelium of the fungus consists of large 
branched threads which are at first olive green and velvety, be- 
coming with age deep brown with a tendency to scale or break 
up into small patches. The hyphge are closely septate, often con- 
sisting of chain-like groups of cells, readily separated one from 
another. Moreover, abundant branching and cementing together 
of these branches may give rise to a kind of false stratum or 
tissue ; anastomosing also occurs. Careful microscopic examina- 
tion has failed to disclose any penetration of the host by this 
organism, and it would appear that it utilizes as a source of 
nutriment only the so-called honeydew resulting from the pres- 
ence of the insects referred to. Certain modified, knob-like 
branches of the hyphae are commonly found, but it is apparent 
that these hypJwpodia serve merely as organs of attachment. 

The propagative stages of this fungus are numerous. Conidia 
of several types, stylospores in pustules, pycnidia, and perithecia 
may be present. The conidia may be simple cells abscised from 
upright hyphae or they may be more highly differentiated compound 
structures. The stylospores are produced from small conidiophores, 
developed within peculiar, elongate, flask-shaped structures. These 
form a conspicuous part of the fungus and are present throughout 
a considerable period of its growth. They are particularly evident 
when branched or variously subdivided, or adherent in groups. 
The pycnidia are relatively minute, but they occur in considerable 
number distributed over the entire surface. The spherical perithecia 
are somewhat larger than the pycnidia and, like those of other 
members of this family, are closed bodies which disseminate their 
spores only upon disintegration. The perithecium may contain 
several short, stout asci with eight dark, elliptical, three-to-four 
septate spores. With the diverse sorts of spore forms mentioned, 
it will be evident that the fungus is rapidly distributed, and conse- 
quently spreads with alarming facility under favorable conditions. 



ASCOMYCETES 2 1 5 

Control. A thorough study of effective methods of control has 
been made under conditions in Florida, and it has been found 
that the most effective preparation there tested is the resin wash. 
This mixture consists, according to Webber, of the following 
ingredients : # 

Resin 20 lb. 

Caustic soda, 98 per cent 4 lb. 

Fish oil, crude 3 lb. 

Water to make 15 gal. 

He prepares this mixture as follows : Place the resin, caustic soda, 
and fish oil in a large kettle. Pour over them 1 3 gallons of water, 
and boil until the resin is thoroughly dissolved, which requires from 
thr6e to ten minutes after boiling has commenced. While hot add 
enough water to make just 1 5 gallons. It is advised to make about 
two sprayings when the insect is in the larval stage. In Florida, 
winter sprayings are important, but a spraying in May is also often 
desirable. In all cases dilute the stock solution with 9 parts of 
water. 

XXI. ERYSIPHACE/E 

BuRRiLL, T. J., and Earle, F. S. Parasitic Fungi of Illinois. 111. State Lab. 

Nat. Hist. 2: 387-432. 1887. 
De Bary, a. Beitrage zur Morphologic u. Physiologic der Pilze 1 (13-14): 

23-75- pi^- 9-12- 
Harper, R. A. Die Entwickelung des Perithcciums bei Sphaerotheca Cas- 

tagnci Ber. d. deut. hot. Ges. 13: 475-481. pi. JQ. 1895. 
Harper, R. A. Sexual Reproduction and the Organization of the Nucleus in 

Certain Mildews. Carnegie Institution of Washington. Publ. 37: 104. 

7 pis. 1905. 
Neger, F. W. Beitrage zur Biologic der Erysipheen. Flora 90 : 221-272. 

1902. 
Reed, G. M. Infection Experiments with Erysiphe graminis De C. Trans. 

Wis. Acad. Sci., etc., 15: 135-162. 1905. 
Reed, G. M. Infection Experiments with the Mildew on Cucurbits, Erysiphe 

Cichoraccarum De C. Trans. Wis. Acad. Sci., etc., 16: 527-547. 1907. 
Salmon, E. S. A Monograph of the Erysiphaceas. Memoirs of the Torrcy 

Bot. Club 9 : 292 pp. g pis. 1900. 
Salmon, E. S. Further Cultural Experiments with Biologic Forms of the 

Erysiphaceae. Ann. Bot. 19 : 125-148. 1905. 
Sands, M. C. Nuclear Structures and Spore Formation in Microsphaera Alni. 

Trans. Wis. Acad. Sci., etc., 15: 733-752. pi. 46. 1907. 
Smith, Grant. The Haustoria of the Erysipheae. Bot. Gaz. 29: 153-184. 

pis. IT, 13. 1900. 

This is a family which, according to the most recent mono- 
graph, includes forty-nine species and eleven varieties of fungi, 



2l6 FUNGOUS DISEASES OF PLANTS 

commonly known as mildews, powdery mildews, and blights 
(Germany, Mehltau ; France, blanc, etc.). Some writers would 
make more than a hundred species of the various forms, the 
species being determined very largely by the hosts upon which 
they occur. The Erysiphace^ are all strictly parasitic, producing 
a considerable, septate, superficial mycelium with a single form 
of conidial spore and a closed perithecium containing the asci. 
This family is such a homogeneous, coherent group that it may 
be treated as a whole, and subsequently a few notes on particularly 
important species may be made. 

Geographical. The various members of this family are, gener- 
ally speaking, most abundant in the north temperate regions of 
the earth, but as a family they are not limited in their distribu- 
tion. Moreover, one species is known to occur as far north as 
Greenland, while another is found in Terra del Fuego. The 
number of species common to America, on the one hand, and to 
Europe, Asia, and Africa, on the other, is approximately the same ; 
but there are supposedly more endemic forms in America than in 
all other countries. Salmon gives fourteen endemic species with 
five varieties for America, while only thirteen species and four 
varieties are known to be endemic in Europe, Asia, and Africa 
combined. 

Climatic relations. The distribution of these fungi is ap- 
parently not closely restricted by slight climatic differences. A 
certain amount of moisture is unquestionably essential to the 
vigorous production of the superficial mycelium characteristic 
of this group, and there are fewer species in dry, exposed 
regions, as, for instance, in the Great Plains regions of the 
United States, than in the more moist Appalachian region. 
Nevertheless, there are a number of species that may be found 
from the extreme north to the extreme south, as well as from 
east to west in both the eastern and western continents. Climatic 
conditions, especially, may determine whether or not a particu- 
lar species may become a devastating disease-producing organism 
or may be classed merely as a fungus of occasional economic im- 
portance. Erysiphe graminis, for instance, is seldom a fungus of 
any consequence in most sections of the United States, while in 
England it may at times cause serious injury to cultivated grasses. 



ASCOMYCETES 



217 



Host plants. The various species and varieties of mildew have 
been reported upon about fifteen hundred species of phanerogams. 
The Hst of hosts includes plants of numerous orders and families. 
A few notable exemptions among plants of normal terrestrial 
habits are Liliaceae, Iridaceae, and some other monocotyledons. 
Furthermore, there are many exceptions among such families, for 
instance, those having the habit of growing under unusually moist 
conditions. Moreover, herbs, shrubs, and trees are more or less 
equally affected, and sometimes a single species of these mildews 
may be found upon plants of all three sorts. 

The leaves are usually the chief parts affected, although some 
species may attack also the twigs, stems, and fruits. As a rule, 
those having the densest mycelia are more persistent and more 
likely to infest all portions of the plant. The Erysiphacese seldom 
cause conspicuous distortions of the host plant. The anatomical 
modifications are therefore secondary in interest to the physio- 
logical effects. 

Cross inoculations. In a very recent summary of the general 
results of cross inoculation in the mildews, Reed states : ^ 

One or more species of five of the genera of the Erysiphaceae have been 
tested for their capacity for infecting host plants other than the one from which 
they came. Podosphasra is the only genus which thus far has not been tested. 
With reference to four genera, Microsphsera, Spheerotheca, Phyllactinia, and 
Uncinula, the data are very meager. The bulk of the work has been done with 
three species of Erysiphe, — E. Cichofacearum, E. graminis^ and E. Poly- 
goni. Even with these species the number of trials is very small in many 
cases, the evidence often resting on a single experiment. Still, sufficient data 
have been accumulated to form the basis of certain at least tentative general 
conclusions. 

So far as investigated, the mildew on the cucurbits, Erysiphe Cichomce- 
arum D. C, is the only one which is shown to be capable of infesting plants 
belonging to more than one genus. My results with this mildew are based on 
a large number of trials, many of them repeated at different times during three 
years, and cannot be questioned. 

There are other cases where the mildew is limited closely to plants of a single 
genus. For example, the mildew on rye is limited to species of the genus Secale. 
The same is true with reference to the bluegrass mildew on species of Poa. 

Several cases also are recorded where the mildew from one species will not 
infect other species of the same genus. Most of these claims, however, rest on 

1 Reed, Geo. M. Infection Experiments with Erysiphe cichoracearum DC. 
Univ. of Wisconsin Built. 250 : 340-416. 1908. 



2l8 



FUNGOUS DISEASES OF PLANTS 



insufficient data. The evidence is more conclusive with reference to the mil- 
dev/ on species of Hordeum and also the one on the Brome grasses. Salmon 
. . . has investigated both of these. The mildew on barley {Hordeum I'ul- 
gare) will infect this species and also Hordeian distichioii^ H. decipiens, 
H. Hexastkhu/n, H. vi/er/nediuin, and H. Zeocriton, but will not pass 
over to Hordeum Jubafum, H. bulbosum^ H. muri?iujn, H. secalinum, 
H. sylvaticnm. In some of these cases, however, the number of trials is 
very small. 

Morphological. With only one or two exceptions (notably 
SpJicErotJieca Mors-nvc£) the superficial mycelium of these plants 

consists of colorless hyphae, 
considerably septate, each 
cell being ordinarily uninu- 
cleate. In all species except 
two, so far as is known, the 
haustoria penetrate the epi- 
dermal cells in the form 
of short, swollen branches. 
However, in one common 
mildew of shrubs and trees 
{/Vivl /actinia Cory lea) hy- 
phal branches grow through 
the stomata and into the 
intercellular spaces. These branches may in turn develop haustoria, 
which enter the cells in contact with this intercellular hypha. As a 
rule conidial production in all forms begins whenever a con- 
siderable mycelium has been developed. These conidia consist, 
quite generally, of a single chain of cylindrical or more or less 
barrel-shaped unicellular portions produced in basipetal order on 
short, erect conidiophores, developed directly from a hyphal cell. 
The conidia are capable of immediate germination, and since 
they are produced in quantity, they frequently give the mealy 
or powdery appearance to the parts affected. They serve for the 
rapid propagation of these fungi. The conidial stage was for a 
long time unconnected with the perithecium form and was then 
known under the form-generic name Oidium, The minute char- 
acteristics of the oidial stages have not been sufficiently studied. 
It is proper to use the name Oidium for any conidial form the 
perfect stage of which is unknown or indetermined. 




Habit of a Powdery Mildew 



ASCOMYCETES 



219 



Perithecia are usually developed during the middle or latter 
part of the growing season. They are produced directly upon 
the mycelium, and the development is interesting and instructive. 
The development, however, can be best followed only by serial 
sections of properly sectioned material. In brief, it may be 
described as follows : Two adjacent cells or hyphae give rise to 
erect branches, one of which is larger and may be designated 
as the oogonium, the other, smaller branch as the antheridium. 
After a basal cell is cut off in each case, and further, a terminal 
antheridial cell in the one case, there is dissolution of a portion 




Fig. 85. Phyllactinia Corylea: Gametes, Fertilization, and 
Development of Perithecium and Young Asci. (After Harper) 

of the wall between the antheridium and the oogonium, migration 
of the antheridial nucleus, and fusion of this with the oogonial 
nucleus (Fig. 85, /;). Subsequently the oogonial cell undergoes sev- 
eral divisions. The last cell but one in this ascogonium contains 
always two nuclei, and these fuse prior to the development of this 
cell as an ascus. This is the case when a single ascus is produced, 
and it is only slightly more complex when many asci result (cf. 
Fig. 85, d-f). Following the fusion of the two gametic nuclei, 
hyphal branches arise from the stalk cell of the oogonium. These 
converge around the oogonium and finally completely inclose 
it. Within this first layer a second layer of hyphse is produced 
in similar manner ; and subsequently, by outgrowths from each of 



2 20 FUNGOUS DISEASES OF PLANTS 



1 



these layers into all available space, smaller hyphae are protruded ; 
thus a compact inclosing body or perithecium is developed. With 
the further growth of the perithecium and the increase in size 
of the ascus, the inner layer and all internal hyphal branches 
are dissolved and appropriated. Meanwhile, the outer layer be- 
comes yellow or brown and forms the true wall of the peri- 
thecium. From the wall cells of the perithecium there are 




Fig. 86. Spore Forms and Appendages of Erysiphace.i; 

a, ErysipJic Polygoni ; l>, PodospJucra Oxyacauih(r ; c, Microsflurra Alni ; c, Pliyllncflnia 
Cory lea ; ^/ and /, Ihuiuula ticcator 

produced, either from the base or from a more or less equatorial 
plane, the characteristic appendages. In a few cases only are 
appendages produced from the apex. At maturity there are one 
or more asci, depending upon the genus, and each ascus con- 
tains normally from two to eight spores, the shape of the ascus 
varying from practically spherical in the one-ascus forms to 
clavate or cylindrical where there are two or many asci. The 
spores are one celled and colorless. As a rule the ascospores 
do not germinate immediately, requiring a period of rest. By 



ASCOMVCETES 221 

the following spring the perithecia are very brittle and are said 
to break open forcibly in water, after which time the ascospores 
readily germinate. The appendages of the perithecium are very 
different in structure from the mycelium in general. The thick 
walls, rigidity of the cells in most genera, and peculiar branching 
indicate that they are specialized structures, and they doubtless 
have an importance in relation to the support of the perithecium 
or the dissemination of this body. 

Classification. The generic subdivisions are based upon the 
number of asci in the perithecium and upon the form and 
method of branching of the appendages. The following key will 
indicate the chief generic characters : 

^■l. Perithecia contain a single ascus. 

1. Appendages simple, flexuous, and undivided at the tip. 

SphcEKotheca 

2. Appendages once or more dichotomously divided at the tip. 

Podosphani 

B. Perithecia containing several to many asci. 

1. Appendages never more than slightly swollen at the base. 

a. Appendages simple or more or less flexuous, or irreg- 

ularly branched, mycelial-like ; without tip peculiar- 
ities Erysip]ie 

b. Appendages usually straight, once or more dichoto- 

mously branched at the tip . . . . Microsphcera 

c. Appendages usually straight and spirally inrolled at the 

tip Unci nil la 

2. Appendages swollen at the base so as to form an enlarged plate. 

Phyllactinia 

XXII. THE GOOSEBERRY MILDEW 
Sphcerotheca Mors-uvcc (Schw.) B. & C. 

Close, C. P. Treatment for Gooseberry Mildew. N. Y. (Geneva) Agl. Exp. 

Sta. Built. 161 : 153-164. pis. 1-2. 1899. 
Eriksson, J. Der amerikanische Stachelbeermehltau in Europa, seine jetzige 

Verbreitung und der Kampf gegen ihn. Zeitsch. f. Pflanzenkr. 16 : 83- 

90. 1906. 
Salmon, E. S. On the Present Aspect of the Epidemic of the American 

Gooseberry Mildew in Europe. Journ. Roy. Hort. Soc. 29 : 102-110. 
fig. 23. 1905. 

This species has long been known as the cause of an im- 
portant disease of gooseberries in the United States. It occurs 



222 



FUNGOUS DISEASES OF PLANTS 



upon the leaves and stems, but particularly upon the berries of 
the host, and it may sometimes cause injury to currant bushes. 
The mycelium is more persistent than that of most Erysiphaceae. 
It is one of the few forms the mycelium of which becomes buff 




Fig. 87. Gooseberry Mildew. (After Close) 

or brown and thick-walled with age. The mycelium forms dense 
circular or effuse patches, sometimes completely covering a berry 
and the adjacent twig. 

The perithecia are imbedded in the dense mycelium. They 
average about 80-ioo/x in diameter and are beset with a few 
light brown, tortuous appendages. A single subglobose ascus 



ASCOMYCETES 



223 



contains relatively large spores. According to Salmon this species 
is indistinguishable from the Sphaerotheca found in Europe upon 
Euphorbia, The latter is, however, not very common in Europe, 
During the summer of 1906 a serious outbreak of gooseberry 
mildew was reported in Europe. The fungus has spread rapidly, 
and the result of this outbreak will undoubtedly afford European 




Fig. 88. Mildew of Peach on Nursery Stock 



investigators an opportunity of testing the validity of the above 
opinion. 

Control. The American gooseberry mildew is one of the most 
difficult of the mildews to control. English varieties of goose- 
berries in America have proved most susceptible, and the best 
results have been obtained by the use of a spray of relatively 
strong potassium sulfide, — i ounce to 2 gallons of water. Spray- 
ing should be given from the time that the buds break open, and 



224 



FUNGOUS DISEASES OF PLANTS 



where the fungus promises to be abundant, it may be necessary 
to repeat the spray every ten or twelve days. Recently it has 
been reported that sulfuric acid may be used to advantage in the 
treatment of the rose mildew, the strength employed being i part 
of strong acid to looo parts of water. This preparation should 
prove serviceable, but it has not been tested for the gooseberry 
mildew. Winter treatment with a lime-sulfur wash has been con- 
sidered desirable as a result of some Canadian experiments. 



XXIII. MILDEW OF PEACH. ROSE MILDEW 



Sphierotheca pannosa (Wallr.) Lev. 



Smith, Erw. F. 

Whipple, O. B. 

7, 2. igo6. 



^' 



Peach Mildew. Journ. Mycology 7 : 90-91. 1892 

Peach Mildew. Colo. Agl. Exp. Sta. Built. 107: 1-7. pis. 



This mildew bears the relation to the peach that PodospJucra 
leucotricha bears to the apple, that is, it is more commonly found 

on nursery stock, and 
then usually only when 
the conditions are moist 
and the stock crowded, 
although occasionally it 
occurs on mature trees 
(Figs. 88 and 89). 

It is as a disease of 
cultivated roses that this 
fungus is best known, 
and most destructive. It 
is widely distributed and 
indeed absent from very few home gardens. There is great differ- 
ence in the susceptibility of different varieties of the rose, and selec- 
tion should lead to resistant strains in many cases. The crimson 
rambler is notably sensitive. 

This mildew covers the leaves, especially the young leaves and 
the vigorous and young shoots, injuring and often arching or 
curling the leaves and deforming the more succulent stems. 
The oidial stage is produced in great profusion, and consequently 
the disease spreads rapidly. Perithecia are not always present. 




Fig. 89. Mildew on Peaches 



ASCOMYCETES 



■25 



Following a moist early summer I have found the perithecia abun- 
dant on old leaves in the shade during a very dry period in late 
summer (Fig. 90). 

Control. Thorough dusting with flowers of sulfur every ten days 
is often sufficient. Ammoniacal copper carbonate is also effective. 




Fig. 90. Rose Mildew, Perithecia Present 

Sulfuric acid i to 1000 has recently been recommended. No ex- 
periments have been reported respecting the use of the " self- 
cooked " lime-sulfur for the rose mildew, but there is reason to 
believe that it may be far more effective than sulfur in this case. 



226 



FUNGOUS DISEASES OF PLANTS 



XXIV. MILDEW OF APPLE AND CHERRY 

Podosphcera O.wacantJue (I)e C.) De Bary 

Fairchild, D. G. Experiments in Preventing Leaf Diseases of Nursery 
Stock. Journ. Mycology 7 : 256. 1894. 

This fungus is common on a large number of rosaceous and 
other plants, including apples, plums, thorn apples, etc. It may 





\ 


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^ 




^^ \ 




^^ 


■•ji^^^lsmBtm: 


UlopM^^' 


■ f'.^^''WWmi. 


W^pHQInl^i ^: ^ 



Fig. 91. Sph^rotheca Humuli on Cultivated Strawberry 
(Photograph by E. H. Favor) 

be considered as a destructive disease in this country chiefly as 
it occurs upon apple nursery stock or upon the cherry (Fig. 92). 
Upon the young apple plants the mycelium is rather dense and 
persistent. Perithecia are from 65 to 90 /a in diameter and the 
appendages, from 4 to 30 in number, are usually from i to 5 
times as long as the diameter of the perithecia. Throughout 
about half of the length of the appendages they are dark brown 
in color, and they are also several times dichotomously branched 
at the tip. A single ascus is given as 58 to 90 by 45 to 75 yu,, con- 
taining normally 8 spores. It is believed that the injurious action 
of this fungus may be easily prevented by the use of copper 
sprays. 

Podosphaera leucotricha (Ell. and Ev.) Salm. In nurseries of 
New York and other eastern states this fungus has, during moist 



ASCOMYCETES 



2 2 7 



seasons, given trouble of serious nature, particularly where the 
nursery stock are planted very close together. The mildew covers 
both surfaces of the leaves and frequently involves the whole 
twig. Spraying with Bordeaux mixture and potassium sulfide is 
effective. 

XXV. POWDERY MILDEW OF PEAS 
Erysiphc Polygoiii De C. 

This fungus is distributed throughout the world. It is the most 
common and one of the most variable of the Erysiphacea^. The 
species has been listed upon con- 
siderably more than three hundred 
hosts of diverse genera and orders. 
Among these the succulent and her- 
baceous plants predominate, but the 
fungus occurs upon some woody 
hosts. 

As a mildew of garden peas {Pismn 
sathunn) this fungus may become a 
nuisance, especially when an attempt 
is made to grow these plants during 
the late summer. It is most preva- 
lent during moist seasons, and more 
destructive in some Atlantic and 
southern states. Upon this host the 
fungus forms a rather dense, persist- 
ent mycelium, frequently covering 
stems, leaves, and pods. The co- 
nidiaare developed in profusion. The 
perithecia, averaging 90 /a in diam- 
eter, are also produced in large num- 
ber during a later period, commonly 
after the plants have begun to diy 

up. When the mildew attacks young plants the crop is generally a 
total loss. The fungus also attacks beans and certain vetches. 

The perithecia contain ordinarily 6-8 asci, each with 2-3 spores. 
The appendages are very variable, even upon the same host, under 
similar conditions. 





f^ 


1 


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1 


E^'a"" ' *" '^j2t' 


'^1 




' ^1 



Fk;. 92. Mildew of Cherry 



228 



f^UNGOUS DISEASES OF PLANTS 



XXVI. MILDEW OF COMPOSITES AND OTHER PLANTS 

Erysiphc Cichoracearmn De C. 

This species of mildew is also widely distributed and occurs 
upon more than two hundred hosts of numerous families. It is 

unusually common upon spe- 
cies of Compositas and in 
general is easily the most 
destructive fungus of these 
hosts. It is also well known 
to the florist upon species 
of phlo.x and to the gar- 
dener upon some varieties 
of cucurbits. 

The fungus is often con- 
fused with the previous spe- 
cies. The perithecia are 
about equal in size, but the 
appendages of this form 
are usually short. The asci 
are numerous (often 10-15), 
and Salmon considers that 
the central specific charac- 
ter lies in the possession of 
two spores. Nevertheless, 
this species is also variable 
in every character, and it 
will not be easy to distin- 
guish morphologically between certain forms of the two species. 




Fig. 93. MicRospH.-ERA Atxr, Persistent 

Form on Oak. (Photograph by Geo. F. 

Atkinson) 



XXVII. MILDEW OF WOODY PLANTS 

Microsphiera Aliii (Wallr.) Wint. 

This variable species is typically a fungus of a variety of 
woody plants. It is common upon amentiferous trees and shrubs, 
but popularly is doubtless best known as the lilac or syringa 
mildew. Upon the lilac the mycelium covers the entire leaf. 
So constant is its occurrence upon this host during the late 



I 



ASCOMYCETES 229 

summer in the United States that one unconsciously associ- 
ates with the Hlac, during that season, a grayish color. Upon 
some hosts, however, the mycelium may form persistent patches 

(Fig- 93). 

The perithecium is generally small, with appendages averag- 
ing i^ times its diameter. These are colorless to light brown in 
part, and 3 to 6 times dichotomously branched. The asci are 
usually 3-8, each containing 4-8 relatively small (18-23 x 10- 
1 2 /i) spores. 

XXVIII. POWDERY MILDEW OF GRAPE 
Undnida iiccator (Schw.) Burr. 

BioLETTi, F. T. Oidium or Powdery Mildew of the Vine. Calif. Agl. Exp. 

Sta. Built. 186: 315-352. figs. I-17. 1907. 
Galloway, B. T. Observations on the Development of Uncinula spiralis. 

Bot. Gaz. 20: 486-491. pl.js-jj. 1895. 
ViALA, P. Les maladies de la vigne, I.e., 2-56. pi. i. figs. i-ig. 1893. . 

This mildew is one which has long been known as an im- 
portant fungous disease in Europe and in America. For many 
years it was supposed that the American plant might not be the 
same as the European, since in the latter country only the oidium 
stage was known, that stage having been described as Oidium 
Tiickcri Berk. It is now certain that the plant in the two coun- 
tries is the same species. 

This species has a light mycelium, which develops on both 
sides of the leaves and sometimes on the flower clusters. In 
the United States it is especially abundant on the leaves in moist 
situations during the late season. It produces a mottled and 
slightly arched condition. During some seasons considerable in- 
jury results to the plant. The conidia are produced in abundance 
and the disease may be rapidly spread. The perithecia vary from 
70 to 1 28 /Li in diameter and are provided with a varying number 
of appendages, usually from 10 to 20 or more, each appendage be- 
ing from one to four times as "long as the diameter of the peri- 
thecium. These appendages are straight or slightly flexuous, 
except as to the uncinate or incurved tip. They may be septate, 
and amber brown in the lower half. There are usually 4-6 asci, 
each containing 4-7 spores. 



2 30 



FUNGOUS DISEASES OF PLANTS 



It is difficult to explain the absence of the perithecial stage 
for so long a period in Europe, and even now when many 
observers would be alert to the presence of such a form, it is 
certain that the occurrence of perithecia is exceptional. For a 
long time it was supposed that the disease was imported to 
Europe from America, as were other grape diseases, but since 
the fungus is also found in Asia, there is no special reason for 
this assumption. The use of the more common fungicides has 
not been so successful in preventing the attacks of this fungus 
as the simple sulfur dust treatment. 



XXIX. POWDERY MILDEW OF WILLOW AND POPLAR 

Uncinuhi Siilicis (De C.) Wint. 

This species is apparently limited in host plants to the two 
genera Salix and Populus, but it occurs upon many species of 

these throughout their 
distribution. The my- 
celium occurs on both 
surfaces, frequently 
evanescent on poplars, 
while often persistent 
and in patch-like areas 
on willow, or covering 
the entire surface {Fig. 
94). On the latter the 
perithecia are also gen- 
erally aggregated. 
They average 135/^ in 
diameter, and are pro- 
vided with numerous 
(often more than 100) 
hyaline appendages, 
the tips of which are 
distinctly uncinate. 
The asci are generally 
about 10, with 4-6 
Fig. 94. rovvDKKY Mildew OF Willow. (Photo- spores, measuring 
graph by Geo. F. Atkinson) 20-26 X lO-I 5 /x. 




ASCOMYCETES 



2^1 



On the willow the area occupied by the mycelium sometimes 
shows a tendency to retain its chlorophyll longer than other por- 
tions of the leaf. This stimulating effect of a parasite is, however, 
best marked in the case of Unciiuila Aceris (De C.) Wint., occur- 
ring on several species of maple (Acer). The yellow leaves in the 
late autumn may show definite green areas, which will be found 
to be the parts of the leaf occupied by the fungus (Fig. 95). 



XXX. COMMON MILDEW OF TREES 
Fhyllactitiia Corylea (Pars.) Ivarst. 

Palla, E. Ueber die Gattung Phyllactinia. Ber. d. deut. hot. (Jes. 17: 64- 

72. pl.s. 1899. 
Salmon, E. S. On Certain Structures in Phyllactinia. Journ. Bot. 37 : 449- 

454. pi. 402. 1899. 

This species of mildew is so distinct from those previously dis- 
cussed that it is by some 
made the type of a sub- 
family. As previously 
stated, no haustoria are 
present, but special seta- 
like branches penetrate 
the host. The perithecium 
is large and provided with 
hyaline, rigid, acicular ap- 
pendages, each with a swol- 
len base. There are many 
asci, containing 2 or 3 
spores (Fig. 86, c). The de- 
velopment of the asci has 
been discussed (Mg. 85). 

This species occurs more 
commonly uj^on shrubs or 
trees, but it is also para- 
sitic upon a limited num- 
ber of herbaceous plants. 
It is known to be distributed throughout the northern hemisphere, 
and is frequently one of the more common of the surface mildews. 




Fig. 95. Yellow Leaf of Maple, with 
Green Areas occui'Ied by Uncinula 



232 FUNGOUS DISEASES OF PLANTS 

XXXI. HYPOCREACE/E 

In this family the myceHum is Hght or bright colored, never 
dark, as is also the stroma when present. Perithecia are also 
colored and vary from a buff or yellow to brown, red, or purple, 
never black. They are usually more or less flask-shaped, free 
upon the substratum, borne upon a mycelial weft (subiculum), 
upon a stroma, or imbedded partially or completely in a stroma 
(well-differentiated perithecial walls are absent in Claviceps, etc.). 
The perithecium possesses a distinct ostiolum or mouth. The 
asci are cylindrical or clavate fusiform. The spores (usually eight) 
are diverse in form, and they sometimes bud within the ascus. Pa- 
raphyses may be present. In general, the family is distinguished 
from other pyrenomycetes only by color and texture. 

In this large family impoitant pathological forms may be se- 
lected from three genera, — Neocosmospora, Nectria, and Claviceps. 

In Neocosmospora there is no true stroma. The colored peri- 
thecia (buff or yellow to red) are clustered or scattered. They 
possess pseudoparenchymatous walls and rather long ostiola. 
The asci contain eight spherical, brown spores, with a distinctly 
wrinkled surface. Conidia are present. 

In the genus Nectria the perithecia are yellowish to brown 
or red, single or grouped, even varying as to the extent of 
the stroma, which is, however, usually tuberculate or wart-like. 
The asci are mostly cylindrical, bearing eight i -septate, usually 
hyaline, elliptical spores. Conidia are common. 

Claviceps is characterized by the development of definite stro- 
mata (sporophores) from a relatively large sclerotium, a stroma 
consisting of a sterile stalk and a fertile head. Within the latter 
(peripherally disposed) the asci are contained in flask-shaped 
structures. There is no definite perithecial wall surrounding the 
ascal conceptacle. The asci are more or less cylindrical and bear 
eight hyaline, continuous, needle-shaped spores. 

Closely related to Claviceps may be mentioned the genus Cor- 
dyceps, including some interesting and striking forms. The major- 
ity occur upon insects, upon which they are parasitic or saprophytic. 
Two species are more or less common parasites of Elaphomyces, 
a truffle-like, hypogeous genus. 



, 



ASCOMYCETES 233 

XXXII. WILT DISEASE OF COTTON, CCJWI'EA, AND 
WATERMELON 

Neocosmospora vasinfeda (Atkinson) Erw. Smith 

Atkinson, Geo. F. Some Diseases of Cotton. III. Frenching. Ala. Exp. 

Sta. Built. 41 : 19-29. 1892. 
Orton, W. a. The Wilt Disease of Cotton and its Control. Div. Veg. Phys. 

and Path., U. S. Dept. Agl. Built. 27: 1-16. ph. 1-14. 1900. 
Orton, W. A. The Wilt Disease of the Cowpea and its Control. Bureau of 

Plant Industry, U. S. Dept. Agl. Built. 17: 1-20. pis. 1-4. 1902. 
Smith, Erw. F. Wilt Disease of Cotton, Watermelon, and Cowpea. Div. 

Veg. Phys. and Path., U. S. Dept. Agl. Built. 17 : 1-53. pis. i-io. 1899. 

This is a fungous disease which has become prominent only 
during the past fifteen years, and it is already a serious foe. The 









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1 


H 


H 




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RJ^^^Hbi 


lA 


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M^ 


iO^H 


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Su&MIk >^' Vr^H 


Wm 


1m 


^1 


9^1 


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Fig. 96. Effects of the Cotton Wilt Fungus in a Field of Non- 
resistant Cotton. (Photograph by W. A. Orton) 

fungus has been studied extensively both in its general biological 
and also in its cultural relationships, but it is not yet certain that 
the forms on the different host plants are properly referable to the 
same species. If so, however, it would certainly seem that these 
hosts have caused at least a racial variation in the parasite. 

Distribution. The wilt disease of cotton is now known to be 
one of the most destructive parasitic diseases of this crop, and it 
is probable that the fungus is distributed practically throughout 



2 34 



FUNGOUS DISEASES OF PLANTS 



the cotton-growing states. It has, however, been found as a most 
serious malady in portions of South Carohna, particularly on the 
sea islands, also in many localities of Georgia, Alabama, and 
Louisiana. It exists also to less extent in other southern states, 
and as far west as Arkansas. The writer has not observed it in 
Texas, although points in all parts of the state were visited in 1 900 
and 1901. On the watermelon the fungus has also been found 
in much the same territory, but most abundant in Virginia and 
South Carolina. The cowpea is affected in many southern states. 




Fig. 97. A Cotton Field Contiguous to that in Fig. 96, but planted 
TO A Resistant Strain of Cotton. (Photograph by W. A. Orton) 

Climatic relations. The wilt diseases do not appear to be to 
any great extent dependent upon climatic conditions. The fungus, 
as will be shown later, is normally to be found in the soil, where 
it may perhaps exist saprophytically for indefinite periods. Neither 
severe temperature changes nor general differences in soil condi- 
tions seem to be of special consequence. Plants in sandy regions 
may be more readily wilted than those in soils more retentive of 
moisture, but, at the same time, the fungus evidently does no 
greater damage ultimately in one soil than in the other. 

Parts of the plant affected. The wilt disease of cotton was 
first described as a " Frenching " (Atkinson). Cotton plants in 



asc:()MYcp:tes 



235 



the heavy soils of central Alabama were somewhat peculiarly 
affected by this fungus. There is first a yellowing and finally 
a drying out of those portions of the leaves farthest from the 
main fibrovascular bundles, that is, between the lobes. Later 
such leaves might fall, or the whole plant might become wilted, 
and finally brown and dead. In other regions of the country the 
"wilting" is much more a characteristic appearance, — the dis- 
ease being scarcely noticeable, except in a stunted condition of 
the plants, until finally wilting results. In general, the disease 




Fig. 98. Cotton Plants of the Same Age: to the Left, Healthy; 
TO the Right, affected by Wilt. (Photograph by W. A. Orton) 



is t}'pically that of a wilt in the case of both cowpeas and water- 
melons. The affected plants have therefore the appearance which 
any plant would have when deprived of its water supply, that is, 
a general wilting and drying up. On cutting the stem, or even 
the leaf petiole of affected cotton, a darkening of the xylem por- 
tion of fibrovascular bundles is shown, and this is an excellent 
indication of the presence of this fungus, since no other disease 
now known discolors the xylem in this way. In some cases 
plants affected and dwarfed show little or none of the characters 
in the stem, yet an examination of the larger root branches and 
even the tap root would show the characteristic appearance. In 



236 



FUNGOUS DISEASES OF PLANTS 



1 



spite of the fact that the disease may sometimes be suddenly 
manifested, yet it is certain that it has a long period of incuba- 
tion, and works very slowly, the final killing of the plant being 
effected only when its water supply is almost completely cut off 
by the filling of almost all of the vessels with the fungous hyphae. 
Resistance of the varieties of the hosts. In almost any infested 
field it will be noticed that there are plants of different degrees of 
resistance toward this fungus. In some plants the fungus is only 
able to effect an entrance into the roots, and each point of infec- 
tion may be the point of origin of several rootlets developed in 
the form of a small tuft. Again, the fungus may extend practi- 
cally throughout the root system and yet fail to invade the stem. 
Finally, the whole plant may sometimes be affected. ■ Two plants 
in the same hill may show great diversity in this relationship. 
Therefore it may be said that all degrees of resistance may be 
found. Experiments conducted by planting many varieties across 
land known to be infected by the disease have shown interesting 
racial variations. Special resistance has been shown by some of 
the Egyptian cottons, although they are not in any case wholly 
resistant. On the other hand, sea island cotton is particularly 
susceptible to this fungus. The most resistant of the upland cot- 
tons thus far reported are certain strains of the variety known as 
Jackson, a limbless sort. The following interesting table (Orton) 
was prepared in 1 900 : 



Table showing Varietal Resistance of Cottons to the 
Wilt Disease 

(The figures denote the comparative resistance of the different races 
on a scale of one thousand.) 



Variety 

Jan7io7ntch 

Mitafifi (average of 3 strains) 

Abbasi 

Jackson (one strain) .... 

Sea Island 

Eldorado 

Texas Wood ...... 

Doughty 

Hawkins Prolific 



Resistance 



565 

559 
479 
453 
233 
227 
162 
148 
142 



Variety 

Brady 

Cook's Long Staple 
Excelsior .... 

Drake 

Jones 

King 

Peterkin .... 

Truitt 

Russell 



127 
124 
104 
90 
88 
83 
71 
71 
55 



ASCOMYCETES 



237 



In the same way as for the cotton, so also in the case of the 
cowpea, resistant races have been found. The most resistant of 
the original varieties tested was the form known as Iron Moun- 
tain, which has since been considerably crossed, and in various 
ways improved. 

The fungus. It has been stated that this fungus is unques- 
tionably very generally distributed and may live indefinitely in 
the soil. This is due to the fact that it is easily propagated 
in a saprophytic manner and may therefore live in all probability 
a long period of time without the intervention of the parasitic 
habit. The fungus gains entrance to the host through the soil, 





Fig. 99. iVeocosmospora vasinfecta. {c after Erw. F. Smith) 
fl, the fungus in xylem of stem ; b and <-, conidial stages from cultures 

and hence through the root system. This is believed to be the 
sole method of infection with the form on cotton and cowpea. 
It is also believed that healthy plants are directly affected with- 
out the assistance of any other organism or mechanical effect 
causing an injury through which the fungus might obtain access. 
The mycelium of the plant is at first found most abundantly in 
the vessels of the xylem (Fig. 99, a) ; but in later stages of the 
disease it may pervade other tissues. Upon the death of the 
plant it comes to the surface along the lines of least resistance ; 
hence it appears lineally distributed in the areas between the 
vertical lines of bast. The fungous hyphae are, as they occur 
in the host plant, yellowish in color, considerably septate, and 
irregularly branched. According to Atkinson conidia may be 



238 



FUNGOUS DISEASES OF PLANTS 




formed within the vessels. These conidia, frequently spoken 
of as microconidia, are at first cylindrical or elliptical, and with- 
out septa ; but they may become slightly curved and once or 
twice septate. These are capable of germination and growth 
within the tissues. On the surface of the host and in culture 
a type of conidia known as macroconidia may be produced in 
quantity. These are lunulate or crescent-shaped and from three 
to five times septate, measuring 30-50 x 4-6 /jl (Fig. 99, r). Upon 

the host the conidio- 
phores arise in loose 
stromatic tufts known 
as sporodochia. In cul- 
ture all gradations be- 
tween the small and 
large conidia may be 
observed. Moreover, an 
"-^' -^ oidium-like stage is 

Fig. 100. Perithecia, Ascus, AND sometimes produced, 

PaRAPHVS.S OK NEOCOSMOSroRA ^^^^ ^^ ^^^ ^.^^^ ^f ^J^J^ 

b (After Erw. F. Smith) 

fungus on the melon 
chlamydospores are not uncommon in old cultures. 

The ascus stage of the fungus has been found both 
on the host plant and in cultures upon steamed potato 
cylinders and other solid media in which ascospores were 
sown. In the case of the cowpea fungus the line of 
culture work so accurately followed out (Smith) has 
shown conclusively that the perithecia may be devel- 
oped from both types of conidia and that the perithe- 
cium is undoubtedly a stage in the development of the wilt 
fungus. As the fungus shows considerable differences on the 
different hosts in regard to the ability to produce perithecia, so 
it shows also a difference in the ease or difficulty with which the 
ascus stage may be produced in artificial cultures from the conid- 
ial stage. The perithecium of the fungus is superficial, more 
or less scattered, flask-shaped (Fig. 100), and frequently orange 
vermilion in color, measuring about 250-350 x 200-300^1. The 
neck may be straight or slightly curved. The ostiolum is closed 
until a late period with well-differentiated cells, and within the 




ASCOMYCETES 239 

neck is lined with periphyses. The perithecia are seated upon 
a sH<2,']it subiculum. 

The wall of the perithecium at maturity is made up of paren- 
chymatous cells more or less polyhedral in form. The asci are 
cylindrical in the spore-bearing portion and measure often loo- 
130X 11-14/U.. ILach ascus contains eight spherical ascospores, 
the latter are brown in color and show at maturity a wrinkled 
exospore or surface. Paraphyses of somewhat peculiar form are 
present. These consist of a loose chain of large cells, as shown 
in Fig. 100, /;. The development of the perithecium, apparently, 
has not been studied in detail. 

Control. It is believed that it will not be possible to control 
such wilt diseases by the use of any toxic substances in the soil. 
Prevention is therefore dependent upon the choice or develop- 
ment of varieties which may be more or less resistant to this 
fungus, as already suggested. Moreover, it will probably be neces- 
sary to look toward the selection of varieties locally resistant, since 
the relation of such varieties to climatic and soil conditions seems 
unquestionably to affect resistance to this fungus. 

Other wilt diseases. Wilt diseases of various other plants have 
been studied and some have been referred provisionally to the spe- 
cies of fungus above described, such diseases, for instance, as the 
stem disease of ginseng, the wilt of the flax, wilt of okra, etc. There 
are, moreover, other fungous diseases due to species of Fusarium 
which may or may not be conidial stages of some species of Neo- 
cosmospora. Examples of such diseases are to be found in the stem 
blight and dry rot of potatoes, caused by Fusanimi oxyspornm. 

XXXIII. A CANKER OF WOODY PLANTS 
Nectria cinnabaritia (Tode) Fr. 

DuRAXD, E. J. A Disease of Currant Canes. Cornell Univ. Agl. Exp. Sta. 

125: 23-38. figs. 1-16. 1897. 
Mavr, H. Ueber den Parasitismus von Nectria cinnabarina. Unters. a. d. 

forst-bot. Institut zu Miinchen 3 : 1-16. pl.i. 1883. 
Wehmer. C. Zum Parasitismus von Nectria cinnabarina Fr. Zeitsch. f. Pflan- 

zenkr. 4: 74-84; Ibid. 5: 268-276. pi. 2. 1894. 

Several important fungous diseases are attributed to different 
species of the genus Nectria. Perhaps the two most destructive 



240 



FUNGOUS DISEASES OF PLANTS 



of these Nectrias are Ncctria cimiabarina (Tode) Fr. and Ncctna 
ditissima Tul. Both of these fungi seem to follow other injuries, 
but either may, after gaining a foothold, spread rapidly from plant 
to plant and be of the nature of an epidemic. 

Distribution. Ncctria cinnabarina is very 
commonly distributed throughout temperate 
regions, at least, and may be found growing 
upon a great variety of hosts. It has been de- 
scribed as the probable cause of an occasion- 
ally destructive disease of currant canes, and 
in the same state it unquestionably exists as 
a parasite upon the pear. The horse-chestnut, 
the china berry, and other trees in various parts 
of the country frequently show the effects of 
its injuries. Durand submits evidence to the 
effect that it is a more or less destructive dis- 
ease to currants throughout New York,^ and 
it has been mentioned as a currant disease in 
other sections of the country, causing affected 
parts to dry up and eventually die. In Europe 
it is also known to cause disease in several 
hosts, all deciduous trees. 

The fungus. The disease seems to infest 
particularly the cambium and soft bast. It is 
therefore unlike its relative Neocosmospora, 
and would seem to be more or less localized, 
gaining entrance, as previously stated, through 
wound areas, and probably killing the twig or 
cane so soon as the latter is girdled. The 
hyphae are closely septate, and large stromatic 
areas are produced upon the epidermis or within the cortex 
(Fig. 102). These rupture the surface layer and appear as tuber- 
culiform stromata, crowned with minute, short, erect, or flexuous 
conidiophores which bear simple, ovate conidia. The general 
appearance of this stroma superficially is that of a pinkish disk. 
The conidial stage appears usually during the summer, and it is 

1 This fungus is certainly not responsible for the common currant cane disease 
of eastern New York. The latter, which is typically a wilt, is discussed later. 





t 

} 

\ 



Fig. loi. Nectria ON 
Currant. (Photo- 
graph by E. J. Durand) 



ASCOMYCETES 



241 



generally followed later in the season by the development of peri- 
thecia, which latter may be differentiated in newly developed 
stroma, or in the stroma which has borne the Tubercularia stage. A 
longitudinal section of the perithecia in a related fungus is shown 
in Fig. 103. The wall of the perithecium consists of an interwoven 
layer of threads having almost a pseudoparenchymatous appearance. 
The asci develop from the base and sides, converging toward the 
apex, each ascus being club-shaped, measuring 60-90 x 8-1 2 /x, and 




Fig. 102. N'ectria c/nnab.ir/n.-u Section ok SroRonocHiuM, 
WITH VouNG Perithecium. (Photograph by E. J. Durand) 

containing eight elliptical spores, which at maturity become two- 
celled by a partition which may divide the spore into two some- 
what unequal parts. The spores are about 14-16 x 5-7/*. 

In artificial culture the mycelium develops rapidly, and usually 
upon almost any of the nutrient media. Upon canes, stems, or 
other solid media the tuberculiform stroma is readily produced. 
Both conidia and ascospores germinate readily. In such cultures 
conidia are produced irregularly upon small branches of the 
hyphae and sometimes abscised more or less directly from large 



242 FUNGOUS DISEASES OF PLANTS 

hyphae as yeast-like conidial cells. The cushion-like masses also 
produce conidia in quantity, Mayr described certain macroconidia 
borne upon small, white stromata preceding the usual cushions on 
the canes ; but Durand was unable to detect such spores. 




Fig. 103. Pleonfctria RHROLmENsrs: A Cluster of Perithecia 
(Photograph by E. J. Durand) 

Control. It would seem that the most practical method of 
control consists in eradicating diseased vines as they appear in 
the spring, the habit and color of the affected canes giving the 
necessary clue to their presence, 

XXXIV. EUROPEAN APPLE CANKER 

Nectria ditissima Tul. 

Hartig, R. Der Krebspilz der Laubholzbaume, Nectria ditissima Tul. Un- 
ters. a. d. forstbotan. Institut Miinchen 1 : 109-128. pi. 6. 1880. 

This disease is apparently widespread in Europe upon the 
apple, and it is not uncommon in the northeastern United States 
upon the same host. It may also appear on the pear. The fungus 
seems to gain entrance to the host through wounds, especially 
hailstone bruises. The mycelium penetrates the bark chiefly, but 



H 



ASCOMYCETES 



243 



to some extent the cambium and the young wood. Much of the 
injured bark peels off, and as the mycehum is perennial, extending 
further each season, large cankers may be produced. 

Unicellular microconidia generally appear first. These are fol- 
lowed, usually on areas killed the previous season, by pale stro- 
matic cushions of fertile hyphae producing macroconidia. The 
latter are twice or more septate, sickle-shaped, and are apparently 
most important in the distribution of the fungus during the 
summer. The perithecia develop late in the season, or the fol- 
lowing spring, arising in clusters on the stromata. 

Control. The fact that this fungus seems to follow other injuries 
suggests that prevention (where preventive measures are necessary), 
especially in the case of susceptible plants, may be practiced by 
simply covering up the wounds with a thorough application of 
Bordeaux mixture or white paint. For example, immediately after 
a hail storm or after pruning it might be desirable to use the 
measures indicated. 

XXXV. STEM ROT OF SWEET POTATO AND EGGPLANT 

Nectria Ipoma'ce Hals. 

Halsted, B. D. The Egg Plant Stem Rot. N. J. Agl. Exp. Sta. Rept. 12: 
281-283. 1891. 

This fungus has been described as the cause of the stem rot 
of the sweet potato {Iponuva Batatas). It is also considered to 
be responsible for a disease marked by the poor development and 
unfruitfulness in eggplant in New Jersey. The affected plants 
manifest the presence of the fungus by a general unhealthfulness, 
finally yellowing and wilting. An examination of the living plants 
may disclose a creamy white mycelium near the base of the stem. 
This mycelium, according to Halsted, bears spores typical of the 
form genus Fusarium, or the macroconidia of other species of 
Nectria, that is, curved, hyaline, and pluriseptate. Later the peri- 
thecial stage appears in clusters at the base of the stem. Genetic 
connection between these spore forms has been verified by arti- 
ficial cultures and by cross inoculation. A comparative study of 
the spore forms indicates that the disease upon sweet potato and 
eggplant is produced by the same fungus. 



244 



FUNGOUS DISEASES OF PLANTS 



XXXVI. ERGOT 

CI aviceps purpurea (Fr.) Tul. 

De Barv, a. Comp. Morphology and Biology of the Fungi, Mycetozoa and 

Bacteria, I.e., pp. 35-39, 220-221, 227-228. 
FisCH, C. Zur Entwickelungsgesch. einiger Ascomyceten. Bot. Zeitg. 40 : 

851-870, 875-897, 899-906. pis. lo-ii. 1882. 
Heald, F. D., and Peters, A. T. Ergot and Ergotism. Neb. Agl. Exp. Sta. 

Press Built. 23 : 1-7. 1906. 
Salmon, D. E. Enzootics of Ergotism. U. S. Dept. Agl. Rept. (1884): 

212-252. pis. 5-(?. 
Stager, R. Infectionsversuche mit Gramineen-bewohnenden Claviceps-arten. 

Bot. zeit. 61 : 111-158. 1903. 
TuLASNE, L. R. Memoire sur I'Ergot des Glumacees. Ann. d. Sci. Nat. 20 

(Sen 3): 5-56. pis. 1-4. 1853. 

The ergot-producing fungus is of more or less 
common occurrence as a disease of rye and other 
grasses. It has never proved a pest of any seri- 
ous importance so far as its effects upon the 
host plant are concerned, but it deserves special 
consideration from the interesting morphological 
characters of the fungus as well as from the na- 
ture and importance of the officinal and toxic 
extract, commonly known as ergotine, which may 
be obtained from a certain stage of the fungus. 
The ergot grains may be accidentally eaten by 
cattle or horses, and no great amount is required 
to cause dangerous poisoning or uterine con- 
traction, paralysis, etc. The fungus is widely 
distributed throughout the United States and 
Europe, and it has been known botanically more 
than half a centur)'. It is probably considerably 
affected by climatic or seasonal conditions, since, 
as will be seen, it must effect an entrance to the 
host plant at a particular time, and the spores 
must therefore be produced in abundance in 
advance of this period. The principal grasses 
affected by the species here discussed are Sccale 
cerealc (r}'e), Lolinm percnne {r)'e grass), Gly- 

ceria nervata, Elynius virgiuicus, and other grasses of more or 

less economic importance. 




Fig. 104. Ergot 
OF Rye 



ASCOMYCKTF.S 245 

The fungus. 'l"he fungus shows an interesting polymorphism, 
first producing a conidial stage upon the o\-ule sac, later the 
sclerotial or true ergot stage in place of the grain, and final!)' 
completing its life cycle by developing cpecial sporophores from 
this sclerotium after a long period of rest has been undergone. 
The fungus is supposed to gain entrance to the host at the base 
of the ovule sac or carpel, penetrating the latter and developing 
through it or over it as a hyphal weft, or primary mycelium, the 
whole structure maintaining the general shape of the ovule sac, 
which is gradually replaced by the fungous body. The surface 
mycelial areas are thrown into folds and numerous short conidio- 
phores arise, bearing small ovate conidia. This is known as the 
sphacelial stage. Insects are attracted to it by a secretion, and 
the spores are by this means 
and by the wind effectively 
disseminated. Meanwhile, a 
dense growth of the fungus 
makes its appearance at the 
base of the affected part and 
gradually enlarges as a firm, 
compact body, or sclerotium. 
It graduallv replaces the area ^'"'- '°5- CL.,yrcEPs pvrpu,.,.,: Sclero- 

a ^ ^ _ TIUM WITH StK(JMATA 

occupied by the sphacelial 

stage, becomes purplish in color, and in time projects be)'ond the 
usual dimensions of the normal ovule sac, pushing forward upon 
its tip the remnant of the sphacelial stage and any portions of style 
and stigma which may remain. The sphacelial stage and the rem- 
nants of the ovule sac are finally brushed away or fall off and the 
mature sclerotium is in the form of a very hard, purplish or brown, 
slightly curved or horn-shaped body, which may attain a length of 
from one half to one and one-half inches (Fig. 105). The develop- 
ment of this sclerotial stage requires about the same length of time 
as is needed for the development of the grain in the normal ovule 
sacs. It is therefore mature at the time that the grain is mature. 

The sclerotium readily falls from its place of production and 
must then undergo a long period of rest before it is in condi- 
tion to be brought to germination. In this particular species ger- 
mination in nature apparently results early the following spring. 




246 



FUNGOUS DISEASES OF PLANTS 



Germination really consists in absorption of water, increase in 
size of the sclerotial mass, and the pushing into growth, some- 
times from many different points on the sclerotium, of compact 
masses of hyphae, which develop into sporo- 
phores. These sporophores may be from one 
fourth to one inch in height, and they bear at 
the summit head-shaped stromata within which 
the perithecia are differentiated. A cross sec- 
tion of the head-shaped stroma is shown in 
Fig. 106, a. 

The sporophore consists of a stalk from one 
half to one inch in length, terminated by a 
capitate enlargement about twice the diameter 
of the stalk portion. In the stromatic tissue of 





Fig. 106. Claviceps purpurea: Section of Stroma and Enlarged 
Perithecium ; also Asci and Spores. (After Tulasne) 



the head numerous perithecia are formed near the periphery. So 
far as is known, a perithecium is developed in two successive 
stages: (i) By the repeated division of a few differentiated cells 
below the surface there results an ellipsoidal pre-ascal tissue. (2) In 
the proximal or basal portion of this cellular body an hymenium 



ASCOMYCETES 



24; 



originates, and the asci to which it gives rise obtain room for com- 
plete development either by forcing the separation of the cells in 
the center of the cellular body or by dissolving some of these. The 
mature perithecium consists of a flask-shaped structure, the mouth 
of which projects, along with the tissues which inclose it, slightly 
beyond the general level (Fig. 106, b). Within the neck of this 
perithecium are to be found many periphy- 
ses. The mature asci are long-clavate. Each 
ascus contains eight filiform spores, averaging 
60-70 /x in length, which issue from the tip 
of the ascus and readily germinate in water 
(Fig. 106, c). 

Control. Proper precautions in the selec- 
tion of the grain seed, together with thorough 
preparation of the land, obviate any danger in 
the case of rye. When detected in the har- 
vested product, the sclerotia must be shaken 
out or the product discarded. When ergot 
appears in abundance on grasses in the pas- 
ture, either the animals must be taken off 
until the ergot falls, or, where possible, the 
grass may be mowed with a machine the blade 
of which may be set high. In the latter case 
subsequent raking may be unnecessary. In 
the central West, ergot is not uncommon on 
the chief pasture crop, blue grass {Poa pratensis). This may not 
be ergot of rye, for besides that species, two ergot-producing fungi 
have been reported on Poa, Claviccps inicroccpJiala (Wallr.) Tul. 
and Claviceps setulosa (Quel.) Sacc.^ 




Fig. 107. UsTiLAGiNoi- 
DEA ON Rice. (Photo- 
graph by II. R. Fulton) 



1 A disease of rice known as green smut is well developed in the rice-growing 
regions of Japan and Louisiana. The effect of the fungus is conspicuous (Fig. 107), 
although only a few grains in a head are affected. The disease has every appear- 
ance externally of being a smut. Brefeld (Unters. a. d. Gesammtg. d. Myk. 12 : 
194) and others have studied this form. Brefeld has studied also more particularly 
a related species on Setciria cnis-an/ece. In both cases the smut-like body is a 
typical sclerotium surrounded by looser hyphas and the dark walled spores. Germi- 
nation studies of the spores seem to indicate that they are conidia, and it has 
been suggested that the fungus may prove to be an ascomycetous form, possibly 
one of the Hypocreales. The species on rice bears the name Cstilaginoidea Otyzcz 
(Cke.) Tak. 



248 FUNGOUS DISEASES OF PLANTS 

XXXVII. DOTHIDIACE/E 

This family includes several hundred species, very few of which, 
however, are of great importance as disease-producing parasites. 
It is characterized by asci arising, apparently, for the most part, 
directly from the stromatic tissue, or at least by a very indistinct 
perithecium, or perithecial wall. They differ from the Hypocreaceae 
especially in the color of the stroma, which is dark to black. The 
most important species, PloivrigJitia morbosa, black knot of the 
plum, is discussed at length, but the genus Phyllachora is important 
from the number of its species and the variety of its hosts. 

'XXXVIII. BLACK KNOT OF PLUMS AND CHERRIES 

Fhnv7-iglitia morbosa (Schw.) Sacc. 

Beach, S. A. Black Knot of Plum and Cherry. N. Y. Agl. Exp. Sta. Built. 

40: 25-34. 1892. 
Farlow, W. G. The Black Knot. Bussey Institution, Built. (1876) : 440-453. 

pis. 4-6. 
Halsted, B. D. Destroy the Black Knot of Plum and Cherry Trees. N. J. 

Agl. Exp. Sta. Built. 78 : 1-14. 1891. 
Humphrey, J. E. The Black Knot of the Plum. Mass. Agl. Exp. Sta. Rept. 

8: 200-210. pi. I. 1890. 
LoDEMAN, E. G. Black Knot. Cornell Univ. Agl. Exp. Sta. Built. 81 : 637- 

657. 1894. 

This is one of the most common and most striking fungous 
diseases of fruit trees in the United States. It has been known 
and described in orchard literature since the early part of the nine- 
teenth century, and the causal fungus was described by Schweinitz 
in 1822. P'or a long time, however, the knot was commonly 
supposed to be caused primarily by insects. A considerable litera- 
ture upon this disease accumulated, but it was not until 1876 that 
a thoroughly competent account of the fungus and its relation to 
the knot was presented. This latter account has remained the 
chief basis of opinions concerning this fungus. 

Geographical. The black knot was apparently at one time con- 
fined largely to the Atlantic seaboard, and was particularly abundant 
only in New England and perhaps New York. It is now known 
to extend across the northern United States to the Pacific Coast, 
although very large portions of the Southwest and large areas of 



ASCOMYCETES 249 

the central West arc jDractically free from this disease. In spite of 
the interchange of plants between Europe and America, the black 
knot has not yet been reported from either England or from the 
continent, and so far as can be ascertained, it is not known to 
occur in other countries. 

Host plants. Very few of the native species of plum or cherry 
are free from this fungus. Among those which suffer particularly 
from the disease may be mentioned the Chickasaw plum {Prunns 
aiigiistifolia), the yellow plum {Piiiiuis avicricana), the wild black 
and red cherries {Prunns scrotina and Pfitnus pcnnsylvanica), 
chokecherry {Prunns virgijiiana), the bird cherry {Prunns avium), 
and the morello varieties {Prunns Ccj-as2is). It is said to occur 
upon other species, but definite records are not at hand. On ac- 
count of the fact that this fungxis attacks wild plums as well as 
cultivated, it is a constant source of danger to plum growing wher- 
ever the native plums abound in neglected places. In certain 
seasons the knot will be found in abundance upon some species 
only, while it will almost entirely omit other hosts. This has 
prompted the opinion that there may be several species or forms 
of the fungus affecting the different hosts. This may be true, but 
it would appear to be almost as well explained by admitting the 
very evident fact that certain hosts are in general more susceptible 
and by assuming that during some seasons particular species may 
be rendered peculiarly susceptible. 

Symptoms. The black knot is a most unsightly disease, con- 
sisting of wart-like hypertrophies or excrescences which may cover 
a considerable area on the twigs and limbs. It is confined entirely 
to the woody parts. The term black knot applied to this disease 
is a very fortunate one, since the deformities take the form of 
elongated blackened knots, usually extending a distance of from 
one or two to four or five inches upon the affected branches. 
For the most part the injury is confined to one side of the 
branch, or at least it does not generally form a complete ring, 
which would effectually cut off the nutriment from the tip portion. 
The first appearance of the knot is usually noted in the spring, 
although it has also been observed to make its appearance in the 
fall (Humphrey). At first it consists of a slight swelling of the 
branch, originating upon any portion whatever, but generally on 



250 



FUNGOUS DISEASES OF PLANTS 



that portion of a limb bearing a side branch. It may arise inde- 
pendently, or near an old knot. As the swelling increases in size 
the bark is broken and the stroma of the fundus then becomes 




Fig. loS. Ploi\-rightia mukbos.i, Black Knot of Plum. (After Longyear) 

evident. By midsummer the knot will have attained full size, and 
from that time until the winter, or as long as the remnants of the 
knot may persist, it will be deep black and carbonaceous in tex- 
ture (Fig. io8, <r). In the case of small twigs which are affected, 
bending may be caused, so that a right angle will be made from 



ASCOMYCETES 



251 



the knotted side. While the smaller twigs are usually affected, 
the knot may also be found upon branches nearly two inches in 
diameter. 

The fungus. The mycelium of the fungus is found during the 
early stages occupying most of the cambium and the bast areas, 
as well as extending throughout the cortex. If the whole cambium 
ring becomes affected the girdling causes the death of the limb be- 
yond. In general, however, the growth of the twig continues, since 
the fungus is confined to one portion of the cambium, growing 
from this layer towards the periphery. The knot itself is made 
up of a mass of tissue, comprising, on the one hand, dense areas 
of the fungus and, on the other, various cells or tissue elements of 
the host. Bast fibers, parenchyma cells, and even vessels may be 
found in this heterogeneous mass in which all of the associations 
of cells normally present have disappeared. This abnormal con- 
dition is apparently brought about by the breaking up of the 
cambium and a resulting development of all the various cell forms 
to which it may give rise in the diverse isolated areas. The dis- 
tribution of the fungous hyphas and the minute anatomy of the 
knot varies upon different hosts. 

During the development of the knot in the spring, small, 
greenish areas may be noticed upon the surface, and later the 
mycelium breaks through the bark from all directions and forms 
upon the surface a very dense layer of closely adherent or pseudo- 
parenchymatous cells. This stromatic fungous layer gives rise to 
conidiophores, which are fiexuous and septate (Fig, 108, c). Each 
conidiophore produces a spore at the tip, and by further growth 
scars, geniculations, or short branches may result. The conidio- 
phores are produced in such quantity that the surface has a vel- 
vety appearance ; they measure from 40-60 x 4-5 ft. The conidia 
are simple, and light brown in color. The period of conidial 
production usually extends from late spring until midsummer. 
Gradually, as the season advances, the velvety surface disappears, 
disclosing a deep black stroma which has been gradually differ- 
entiated. From an early period there can be observed with a 
hand lens certain papillae which locate the forming perithecia 
in this stromatic area. The later conidiophores are therefore 
still evident on the surface when developing perithecia are easily 



252 FUNGOUS DISEASES OF PLANTS 

demonstrated through sections. The perithecium contains at ma- 
turity the ascospores, or perfect stage, of this fungus. Owing to 
the dense structure of the knot, it is almost impossible to follow 
closely the stages of development in the hymenial tissue and in 
the formation of the asci. The asci, at any rate, develop during 
the winter, and the spores are ripe during midwinter or later, de- 
pending upon the region. Each mature ascus is about 120/x in 
length, and contains eight spores, the spores being two-celled by 
a cross wall which separates unequal portions. They may be vari- 
ously arranged in the ascus but are often obliquely uniseriate, each 
being 16-20 x 8-iO/u.. Paraphyses are always present. These are 
filiform, nonseptate structures with a slightly enlarged tip. Other 
spore stages, a stylosporic and a pycnidial stage, have been found 
associated with the two already described, but they are not of com- 
mon occurrence, and may not represent fixed and common stages 
in the life history of this species. 

The conidia and the ascospores germinate in plum juice or 
upon various nutrient media, and pure cultures may be readily 
made upon solid media. The spores also germinate in water. 
Humphrey succeeded in developing a pycnidial form upon nutri- 
ent gelatin which differed from any stage of the fungus found 
on its natural hosts. 

In spite of the good work which has been done upon the de- 
velopment of this fungus, there is opportunity for much more 
careful morphological study. It would be necessary to study the 
plant upon different hosts and upon various culture media in pure 
cultures in order to determine the ultimate relationships of the 
different spore forms which have thus far been described. 

Control. It is evident that since the conidial stage is produced 
abundantly during late spring and early summer, pruning out of 
the developing knots just prior to the season mentioned would 
largely control the spread of this fungus by the conidial stage. 
A similar careful pruning should be given prior to the develop- 
ment of the ascospores, if any knots have been overlooked. It 
would be well, however, to make several jDrunings during the year 
if this method of eradication alone is practiced. The suppression 
of black knot has been a subject of legislation in many states, and 
in those in which it is fairly well under control, pruning is usually 



asc()mycetp:s 253 

sufficient to prevent the spread from occasional outbreaks. Since, 
however, wild plums and cherries everywhere may be affected, 
eradication is difficult. In many regions the fungus is so com- 
mon and so persistent that it is necessary to take additional pre- 
cautions. Spraying with Bordeaux mixture has been advised, and 
where spraying is given, one application should be made during 
the late winter and one when the buds begin to swell. This latter 
should be followed by two or three subsequent applications as may 
seem necessary. It has been thoroughly demonstrated, however, 
that the disease is controllable, and when cooperation is given, 
eradication in large areas is perhaps possible. 

XXXIX. SPHv^RIALES 

The sphasriaceous Ascomycetes constitute an order (sometimes 
considered a suborder) containing more species than perhaps any 
other equivalent natural group of the fungi. The great majority 
are saprophytic in habit, occurring upon decaying twigs, leaves, 
and, in fact, upon practically all kinds of vegetable matter, or 
upon the soil. There are some notable parasitic species, but 
these are relatively inconsiderable as compared with the great 
number of saprophytes. 

The mycelium may be light or dark colored, usually the latter, 
and the perithecia show very diverse characters with respect to 
texture and form of the ostiolum, as also with relation to the sub- 
stratum and stroma. They may be free, slightly connected by a 
scant subiculum, or more or less imbedded in a stromatic tissue 
of variable texture. The perithecia vary from membranous to 
carbonaceous, delicate, tough, or brittle, and the ostiolum may 
be merely a circular aperture, a slight papillate opening, or a 
long beak. What has been said of conidial stages under the 
Ascomycetes in general applies in particular to this group, these 
stages being manifold, so far as the method of conidiospore pro- 
duction is concerned. 

This order is commonly subdivided into eighteen families, 
which differ from one another, however, in characters so slight 
that a brief key of those which are here to be considered may 
be sufficiently descriptive. 



254 fun(tOUS diseases of plants 

A. No stroma present; perithecia for the most part completely immersed 

in the substratum, or finally becoming more or less free by the rup- 
ture of the inclosing matrix (epidermis in the parasitic forms). 

1. Perithecia for the most part without distinct beak, tough but 

not carbonaceous. 

a. Asci arising in groups from the perithecial wall with- 

out intervening paraphyses . MycospJicerellaceiE 
(Represented by Guignafdia and Mycosphcerella^ 

b. Asci arising from the base of the perithecium and 

not in groups. Paraphyses present. Pleosporacecc 
(Represented by Venfuria.) 

2. Perithecia carbonaceous or tough leathery, as a rule with 

a distinct beak. Asci thickened at the apex, commonly 

breaking open by a pore GiiomoniacecE 

(Represented by the genera GloniereUa and Giiomonia.) 

B. No stroma present ; perithecia free upon the substratum, or surrounded 

at the base by a dense mycelial mat Spliariacecr 

(Represented by Rosellinia.) 

C. Stroma present, consisting of intermixed and modified fungous and host 

elements ; perithecia imbedded ; pycnidia present . . . I ^alsacece 
(Represented by Diaporthe.) 

D. Stroma present, consisting of fungous hyphae only ; perithecia im- 

mersed Xylariacece 

(Represented by lYioju/nilaria.) 



XL. BLACK ROT OF CxRAPES 
Guigna)-dia Bidwellii (Ell.) Viala &: Ravaz 

Edson, a. W. The Black Rot of the Grape in North Carolina and Its Treat- 
ment. N. C. Agl. Exp. Sta. Built. 185 : 131-150. 1903. 

Jaczewski, a. V. ijber die Pilze, welche die Krankheit der Weinreben 
"Black Rot" verursachen. Zeitsch. f. Pflanzenkr. 10: 257-267. figs. 
1-8. 1900. 

Reddick, D. The Black-Rot of the Grape and Its Control. Cornell Lhiiv. 
Agl. Exp. Sta. Built. 253: 367-388. figs. 177-187. 1908. 

Report on Experiments made in 1888 in the Treatment of the Downy Mil- 
dew and Black Rot of the Grape \'ine. U. S. Dept. Agl. Bot. Div. 
Built. 10: 1-61. 1S89. 

SCRIBNER, F. L. The Fungous Diseases of the Grape Vine. Bot. Div. U. S. 
Dept. Agl. Built. 2 : 28-34. ///. 1886. 

SCRIBNER, F. L. Fungous Diseases of the Grape and Other Plants and their 
Treatment. 1890. 

Viala, P. Les maladies de la vigne. 595 pp. ig pis. sgofigs. (Black Rot: 
156-203. //. 4. figs. 48-J4.) 1893. Montpellier et Paris. 

Viala, P., et Ferrouillat, P. Manuel pratique pour le traitement des mal- 
adies de la vigne. 1888. 



II 



ASCOMYCETES 



255 



Distribution. The most serious menace to grape growing in 
most sections of the United States is the well-known black rot, 
a fungus of American origin, the effects of which have been 
known for considerably more than half a century. 

The black rot is now very generally distributed throughout 
the grape-growing sections of the United States and is reckoned 
with as a constant foe wherever susceptible varieties are grown. 
It is supposed to have been introduced into France somewhat 
more than twenty years ago, and it is now common in other sec- 
tions of Europe, and throughout the Mediterranean region. Its 
ravages are more serious under the conditions which commonly 




Fig. 109. Black Rot of Grate, showing Progress of the Disease 
(Photograph by Donald Reddick) 

encourage the growth of parasitic fungi, that is, moist, warm days, 
or the muggy weather of midsummer, being particularly favorable 
for its rapid development and spread. 

Symptoms. The black rot fungus occurs upon the berries and 
leaves (Figs, no, in), also upon fruit pedicels, and sometimes 
upon young canes. The berries are most severely affected, al- 
though the disease may first be seen upon the leaves. Upon the 
latter it appears as sharply defined, nearly circular, brown spots. 
Sooner or later small pycnidia may be found at the centers of 
these spots. The berries are not ordinarily attacked until about 
two thirds grown. The first sign of injury is the appearance of 
a purplish or livid brown spot, which normally spreads over the 
whole surface of the berry. The affected fruit gradually becomes 



256 



FUNGOUS DISEASES OF PLANTS 



darker in color, and pycnidia, appearing as black papillae, may be 
produced over the entire surface. At this stage the effects of the 
fungus are therefore unmistakable. Later the fruit shrivels in a 
characteristic manner, but does not, as a rule, fall or shell. The 
berries on bunches thus affected may hang on the vines through- 
out the season. The pycnidia may also be easily observed with 
the unaided eye upon the dried berries. 

Susceptibility of varieties. It seems to be the general experi- 
ence that practically all of the more commonly cultivated varieties 

of grapes, particularly, how- 
ever, the dark colored va- 
rieties, including Concord, 
Hartford, Roger's Hybrids, 
etc., are susceptible. In some 
districts certain light col- 
ored varieties are more re- 
sistant and the Scuppernong 
is practically free from 
attack. In this case, how- 
ever, as in many others 
already mentioned, there is 
a great difference in the re- 
sistance of varieties accord- 
ing to their environmental 
conditions. For all commer- 
cial purposes grape growing 
would be impossible in most 
localities, on account of the 
great losses entailed, if the 
disease were not practically controllable by spraying operations. 

The fungus. The mycelium of this fungus is found in the 
outer portions of affected berries, but mycelium is never abun- 
dant. Under favorable weather conditions only about one week 
may be required from the time of infection to the development of 
the pycnidia, — ordinarily 8-12 days are necessary. The pycnidia 
have long been known under the name PJioma Jivicola B. & C. 
Upon the leaves the pycnidial stage has passed under the name 
Phyllosticta Labrusae. The pycnidium develops from a stromatic 




Fig. no. Grapes affected i5Y Black Rot 
(Photograph by F. C. Stewart) 



i 



ASCOMYCETES 



257 



mass of mycelium which arises hencath the epidermis. It is 
broadly elliptical, with a rather thick wall and no indication of a 
beak (Fig. 112, a). The conidiophores are short and simple, bear- 
ing spores — ovate or elliptical — measuring ordinarily 8— 10 x 7- 
8/i. In moist weather the spores are pushed out in vermiform 




Fig. III. Phyllosticta Stage of the Black Rot Fungus 
(Photograph by H. H. Whetzel) 

masses and upon dissemination they are capable of immediate 
germination. Accompanying these pycnidia (the spores of which 
are frequently known as stylospores) there may be found some- 
what smaller, more nearly spherical pycnidia (commonly but un- 
fortunately known as spermagonia). The latter contain relatively 
long filiform conidiophores converging towards the center, and 



258 



FUNGOUS DISEASES OF PLANTS 



upon these are borne minute, cylindrical, or slightly curved 
conidia. It is, however, doubtful if this last mentioned pycnidial 
form is either common or of much consequence in the rapid 
distribution of the fungus. 

The ascigerous stage was first found and named in 1880, and 
since that time the name has been more frequently changed than 
has the fungus been accurately studied. It is stated that the asci 
were first found upon berries which had hung upon the vines 
during the winter and had subsequently been dropped into water 
for a few days. Since that time the perfect stage (Fig. 112,^) has 

been frequently detected on af- 
fected berries which have lain 
under favorable conditions dur- 
ing the spring months, as when 
covered by leaves and grass. It 
would seem, however, that very 
few observations have been 
systematically made to deter- 
mine the time of development 
of the ascospores. The asci 
may apparently develop in per- 
ithecia which have previously 
served as pycnidia, or resting 
stromatic masses may give rise 
to the perithecia directly. The 
asci are broadly clavate, some- 
times slightly curved, and they 
contain eight nonseptate, hyaline spores, the latter measuring 12- 
17 X 4.5-5 A*- They are generally ovate. 

Control. The most efficient remedy for the black rot is 
Bordeaux mixture. After cleaning the vineyard as well as possi- 
ble of the pruned and diseased litter, the old berries being 
covered by early plowing, Bordeaux should be thoroughly applied, 
covering vines, posts, and trellis just as the buds are swelling in 
the early spring. A second application is made as the buds 
unfold, and subsequently the vines should be sprayed about every 
two weeks, until five or six applications have been made. The 
nature of the season, however, will determine how late it will be 




Fig. 112. GuiGNARDiA BiDiriii.Li I; Sec- 
tions OF Phoma and Ascigerous 
Stages 



II 



ASCOMYCETES 259 

necessary to continue such operations. To one familiar with the 
hfe history of the fungus it is evident that the time for spraying 
will be governed by the condition in which the fungus is found. 
When no spores are being produced spraying may be unneces- 
sary ; when spores are being produced in quantity weekly spray- 
ings may be demanded. Moreover, when it is necessary to spray 
during the late season, ammoniacal copper carbonate may be sub- 
stituted for the Bordeaux, in order to avoid the unattractive dis- 
coloration of the fmit. 

XLI. CRANBERRY SCALD 

Gi/ig>ian/ia Jairi/iii Shear 

Shear, C. L. Cranberry Diseases. Bur. Plant Ind., U. S. Dept. Agl. Built. 
110: 1-64. pis. 1,2. 1907. 

Distribution and effects. Under the name of scald a number 
of fungi affect the cranberry, but the most important diseases of 
this plant are produced by the fungus above mentioned. It has 
been estimated that the annual loss from cranberry scald is about 
^200,000, and that this fungus is responsible for the greater part 
of this amount. The disease is more common toward the south- 
ern limit of cranberry culture, especially from New Jersey south- 
ward, whereas further to the north, as in Massachusetts, it is far 
less destructive. 

The fungus may attack very young fruit, and even flowers, 
which promptly shrivel and die. The latter effect is commonly 
known as "blast." Upon such parts the pycnidial stage of the 
fungus is commonly found. The term scald is applied partic- 
ularly to the effect upon the berry, which begins, according to 
Shear, as a small watery spot upon the surface of young fruit. 
This spot may remain small under certain conditions, and again 
it spreads quickly, often concentrically, rendering the whole berry 
soft, and sometimes marked by rings. This, however, is not a 
definite character. There is little superficial evidence of the pres- 
ence of the fungus, unless the berries are attacked before they are 
half grown, when they may promptly shrivel and develop the 
pycnidia of the fungus. The fungus also affects the leaves, and 
when found upon these parts, brown spots, irregular in outline, 



26o 



FUNGOUS DISEASES OF PLANTS 



are produced within which areas the pycnidia may be found. 
Cuttings may also be affected. 

The fungus. The pycnidial stage is a characteristic Phoma or 
Phyllosticta, lOO to i20/x in diameter, as shown in Fig. 113. 
These are distributed over the affected surfaces, and produce 
abundant conidia, which are hyahne, obovoidal, frequently trun- 
cated at the apex, measuring 10.5-13.5 x 5-6 /x. The conidia are 
appendaged, and they are expelled from the perithecium much as 
in the black rot of the grape. The ascogenous form is less com- 
monly found. In this the perithecia are much as those already 
described, except that the wall is denser and they bear only asci. 
The latter are more or less clavate, with a total length of from 





Fig. 113. GuiGNARD/A K/cc/.v// ON Cranberry: Pycnidial and Ascigeruus 
Stages. (After Shear) 

60 to 80 />t. The spores are hyaline when young, and tinted when 
old. They are described as elliptical or subrhomboidal in form, 
with granular contents (Fig. 113, b). 

This fungus has been carefully cultivated, cultures being made 
from both stages and from hyphae, as well as from the tissue of 
the host beneath the scalded area upon the berries. It is reported 
to grow well upon acid and neutral media, and especially vigorous 
upon corn meal in various combinations. The pycnidial form has 
been produced in culture ; yet in many cultures the conidia are 
not produced in the perithecia, but the latter remains as a more 
or less sclerotial organ. The ascogenous form, however, has been 
secured in cultures from both berries and leaves. After a few 
generations in culture tubes, the fungus appeared to lose con- 
siderably in vitality, and frequently developed no spore forms 



ASCOMYCETES 26 1 

after one or two generations. In general, the conditions under 
which growth takes place do not seem to affect to any great ex- 
tent production of fruiting stages. It is believed also that after 
the fungus has penetrated the host it may remain under favorable 
conditions inactive for some time, and that therefore the period of 
incubation may be long or short, depending upon conditions. The 
ascogenous form has not been found abundantly in nature, and 
may not be very important in the distribution of the fungus. 

Control. Prevention should concern itself particularly with 
sanitation, including the renovation of the cranberry bog, proper 
regulation of the water supply, and the development of disease- 
resistant strains. Spraying with Bordeaux mixture has also proved 
of value. In spraying, however, the addition of substances ren- 
dering the mixture more adhesive is necessary. 

XLII. LEAF SPOT OF STRAWBERRY 

Mycosphcerella Fragariw ("rul.) Lindau 

Dudley, W. R. On the Strawberry Leaf-Spot. Cornell Agl. Exp. Sta. Built. 

14: 171-184. 1889. 
ScKHiXER, F. L. Strawberry Leaf Blight. LI. S. Dept. Agl. Rept. (1887): 

334-341- pf- I- 

One of the diseases of the strawberry most frequently met with 
is that commonly known as the strawberry leaf spot. The disease 
makes its appearance in the form of small, discolored spots, ap- 
pearing upon the leaves most abundantly about the time of flower- 
ing (Fig. 114). At first these spots are of a reddish or purplish 
tint, but as they increase in size the center becomes pale and may 
be quite white when the death of the tissues has ensued. This 
white central area is ordinarily bordered by a zone of red and 
purple in different shades. These spots are irregularly distributed 
over the leaves, and when numerous they may coalesce. All of 
the cultivated varieties of strawberries may be affected, although 
there is considerable difference in the degree of susceptibility. 
Among some of the berries most susceptible in the northeastern 
United States may be mentioned the Hunn and the Beeder 
Wood. Susceptibility of a variety varies, however, when culti- 
vated under different conditions. Marshall and Brandywine have 
often proved very resistant. 



262 



FUNGOUS DISEASES OF PLANTS 



The fungus. The life history of the fungus has been con- 
siderably studied, and it is probable that some spore stages which 
have been described are not at any rate common stages in the 
life cycle. In general, two spore-producing stages may be found, 
the conidial and the ascigerous stages. The conidial stage has 
been described as Ravudaria Tulasuci. This appears in early 
summer, as a rule, or so soon as the pale centers of the spots 
have been developed. Small, tuberculate stromatic masses are 
produced upon the mycelium beneath the epidermis, and from 
these arise a small group of simple hyphae, which rupture the 




Fig. 114. Leaf Spot of Strawberry 

epidermis and produce conidia which may become one or several 
times septate. The conidia, according to Dudley, measure 20- 
40 X 3-5/^ (Fig. 115, n). 

The ascigerous stage is not so commonly found and is in no 
case developed until late summer. A membranous perithecium, 
characteristic of this family, is then produced within the leaf, al- 
though at maturity a considerable part of the perithecium may be 
exposed. Relatively few asci are developed, the asci containing 
invariably eight hyaline, uniseptate spores with acute tips (Fig. 115). 
It would appear that the spores are not ordinarily mature until 
late winter, or at least not ejected until that time. Moreover, 



i 




ASCOMYCETES 263 

hibernation is supposed to be effected in some cases by means 
of the tuberculate stromata, which retain their vitahty and serve as 
minute sclerotia, germinating the following spring. The asci 
average 40 /x long, and the spores 
measure about i 5 X 3-4 fi. 

Control. Healthy plants only 
should be set, and all spotted 
leaves should be pinched off. 
A thorough spraying with Bor- a b 

deaux mixture may be given Fic 115. yi/}'co.v/'//.^-A'//i/_./ /"/e.-ZG./Av.-/?, 

1 r ,1 n 1 CONIDIAL AND ASCIGEROUS STAGES 

before the nowers are open, when 

necessary. If the disease is serious or disastrous late in the season, 
its reappearance the next year may be delayed and to some extent 
averted by mowing off the leaves and burning over the bed. 

XLIII. LEAF-SPLITTING BLIGHT OF SUGAR CANE 

Alycosphcerella stmtiformans Cobb 

Cobb, N. A. Fungous Maladies of the Sugar Cane. III. Leaf-Splitting 
Blight. Hawaiian Sugar Planters Exp. Sta. Built. 5: 93-106. 1906. 

This is the name provisionally applied to a fungus which 
causes a peculiar leaf-splitting of sugar cane in portions of the 
Hawaiian Islands. The leaves are split, and in severe cases 
reduced to shreds. The ascogenous stage alone has been re- 
ported. The perithecia are produced abundantly. Diseased stalks 
should not be planted, and all leaf trash from an affected field 
should be destroyed. What appear to be related species of fungi 
have been described as injurious to cane in Java and in La Plata, 
Argentina. 

Mycosphaerella Cerasella Aderh.^ is considered to be the ascog- 
enous form of Ccrcospora Cerasella Sacc, well known upon the 
leaves of cherry, sometimes producing a shot hole effect similar 
to that which may follow any leaf spot fungus parasitic upon 
species of Prunus. 

1 Aderhold, R. Mycosphaerella cerasella n. spec, die Perithecienform von 
Cercospora cerasella Sacc, und ihre Entwicklung. Ber. d. deut. bet. .(Jes. 18: 
246-249. 1900. 



264 



FUNGOUS DISEASES OF PLANTS 



XLIV. APPLE SCAB AND PEAR SCAB 

Veil f una Poiiii (Fr.) Wint. and ]^eutnna Pyriiia Aderh. 

Aderhold, Rud. Die Fusicladien unserer Obstbaume. Landwsch. Jahrb. 

25: 875-914. pis. 2g-ji. 1896; Ibid. 29 : 541-587. pis. g-12. 1900. 
Beach, S. A. Experiments in Preventing Pear Scab in 1893. N. Y. Agl. 

Exp. Sta. Built. 67: 183-204. 
Clinton, G. P. Apple Scab. 111. Agl. Exp. Sta. Built. 67: 109-156. 1901. 

(Good bibliography.) 
DuGGAR, B. M. Some Important Pear Diseases. Cornell Agl. Exp. Sta. 

Built. 145: 616-622. figs. 168-iyo. 1898. 
Lawrence, W. H. The Apple Scab in Western Washington. Washington 

Agl. Exp. Sta. Built. 64: 1-24. pis. 1,2. 1904. 
Smith, Ralph E. Pear Scab. Calif. Agl. Exp. Sta. Built. 163: i-iS. figs. 

1-9. 1905. 

Two important fungous diseases popularly known as apple and 
pear scab have received at the hands of both mycologists and 

horticulturists considerable 
attention within the past 
thirty years. The fungi 
causing these diseases are 
very closely related, al- 
though quite generally re- 
ferred to two distinct 
species. The conidial form 
of each of these fungi was 
first found parasitic upon 
its respective host ; hence 
these fungi have long been 
known by the names of 
these conidial forms, Fjisi- 
cl a dill 1)1 dcndriticjini and 
Fitsicladinm Py rin ii m . 
More recently an ascomy- 
cetous fungus, Vcntiiria Poiiii, has been found to constitute the 
perfect stage of the apple scab organism, and a related perithecial 
form, ]^ciitnria Pyrina, has been connected with the pear scab 
fungus. The perithecial stages develop saprophytically, a phe- 
nomenon characteristic of many Ascomycetes. 

Distribution and climatic relations. In the United States both 
the scab of the apple and of the pear are widely distributed. 




Fir.. 116. A Severe Attack ok Peak Scah 
ON Flemish Beauty 



ASCOMYCETES 265 

Moreover, the data at hand seem to indicate that they occur 
in all countries in which the host plants are commercially grown. 
These fungi are apparently of economic importance in all sec- 
tions of the United States where the weather may be cool and 
damp during portions of the spring and summer. In the northern 
portion of the United States it has received particular attention 
at the agricultural experiment stations of Vermont, New York, 
Illinois, also California, thus indicating a very general distribu- 
tion. It is, however, believed to be equally distributed in the 
Southeast, but in that section it has received less attention, per- 
haps on account of the fact that the commercial output of these 
fruits has not been a factor of such importance. In the past few 



■ 


^^i^ 


i^^i 




■■■■ 


■ 


W^TM 






^^^^^^H 


p 






.'^hH 




W 


>. • ^ '^^SsBf 4lfiL M 


^M^Hl 






ii 


■A^ 




[3 





Fig. 117. The Effects ok Apple Scab during a Moist Season 

years these diseases have become a menace on the Pacific Slope. 
All investigators, however, are agreed that cool, moist weather 
either in spring or summer encourages the rapid spread of the 
fungus, while hot winds quickly suppress it. 

Losses. It is not easy to estimate the average losses from these 
fungi, and this is particularly true on account of the fact that the 
scab fungi are more or less superficial in their effects. In severe 
cases the fruit is wholly unmarketable, but in too many cases 
scabby fruit is regularly put upon the market and the reduced 
prices which it brings are not estimated. During seasons favor- 
able for the fungus, probably one year in two, the losses in many 
sections of the country amount to a reduction in price or total 
destruction of from 25 to 50 per cent of the entire crop. 



266 



FUNGOUS DISEASES OF PLANTS 



The relation of host and fungus. These fungi commonly 
affect fruit and leaves, but they may also be found upon leaf 
stalks, flowers, and "twigs. Upon the leaves (Fig. ii8) in each 
case the spots are more abundant, as a rule, upon the lower 
surface. Where the fungus is made evident by an olivaceous, 
velvety, superficial growth, or when the disease is very abundant, 
both surfaces of the leaf may be covered and considerable curling 




Vie. ii8. Ai'i'LK Scab on Leaves: Different Types of Infection 



may result. Upon the fruit there are at first small, circular, oli- 
vaceous spots, especially upon the pear, but as a rule the appear- 
ance changes as the fungus spreads, the epidermis is killed, and 
the familiar scabby spots are produced. At times practically the 
whole fruit may show indications of the fungous growth, and a 
general puckering of the tissues may result in an abnormal form 
of the fruit. Some varieties of pear may develop cracks or 
fissures extending halfway to the core. Fig. ii6 shows a severe 
attack of scab on Flemish Beauty. 



ASCOMYCETES 



267 



There are probably no varieties of the pear or apple which 
are entirely free from scab. Nevertheless, there is a great dif- 
ference in susceptibility. In New York, Flemish Beauty, vSum- 
mer Doyenne, Duchess, Clairgeau, Sheldon, Seckel, Anjou, and 
Lawrence have been reported as more generally affected than 
Le Conte, Kieffer, and Bartlett. In California the later varieties 
like Winter Nellis and Easter Beurre are said to be more sus- 
ceptible than the Bartlett, which, however, is only resistant to 
an intermediate degree. The susceptibility of different varieties 
of apple to the apple scab seems to vary considerably according 





7: 




m 


CxS- 



Fig. 119. CoNiDiAL Stage: Fusicladium of the Pear Scais F'ungus 

to the region in which grown, yet nearly all of the standard 
varieties may be affected during seasons favorable to the fungus. 
The fungus. The spores of the Fusicladium stage germinate 
readily in water and develop a short germ tube, or sometimes 
two germ tubes. The germ tube sometimes forms a dark spore- 
like structure, if the conditions are not favorable for further rapid 
growth. This structure is scarcely in the nature of an appres- 
sorium, and may be considered a resting stage, which will grow 
out into mycelium under favorable conditions. It is believed that 
the mycelium of these two species of fungi develops for a short 
time superficially, then penetrates the epidermis in some way. 
At any rate, the mycelium is found at a very early stage beneath 



268 FUNGOUS DISEASES OF PLANTS 

the epidermis, and between the epidermis and cuticle. In these 
situations it spreads slowly. According to some writers the prin- 
cipal development at first is immediately beneath the cuticle. 
That is particularly true, according to reported observations, on 
the leaves. On the fruit, however, both the cuticle and the epi- 
dermis are soon broken and disappear as the spot becomes scabby 
in appearance. Upon the pear I have quite generally found the 
mycelium to be subepidermal at the edge of the scabby spots. It 
may form a layer several times as thick as the diameter of the hyphae, 
and as the epidermis wears off, this mycelial layer is exposed, and 
beneath this the cells of the host may become corky, as shown 
in Fig. 119. The mycelium is olivaceous or sometimes reddish- 
brown in color, closely septate, sinuous and irregular in branching. 




Fig. 120. Germinating Spores of Fusicladium 

The olivaceous growth on the surfaces of the fruits, leaves, and 
twigs is, however, made up veiy largely of the short, erect conidio- 
phores. These conidiophores arise from the subcuticular or sub- 
epidermal mycelium, break the cuticle if the latter is still intact, 
and a spore is soon developed at the tip of each, A spore may 
be borne when the conidiophore has attained a length of four or 
five times its diameter. However, when this spore is abscised, 
the conidiophore grows further, leaving a slight knee or other 
evidence indicating the point where the previous spore was borne. 
In this manner many successive conidia may be produced, and 
the conidiophore therefore becomes flexuous and irregular. It 
may also become septate in time. The conidia on both hosts 
measure ordinarily 28-30 x 7-9/^. They are more or less ovate 
in form, the basal end being more truncate. They are ordinarily 
continuous but may become once septate with age. The color is 
fuliginous or olivaceous, sometimes having a slight reddish tint. 



ASCOMYCETES 269 

According to Clinton, tlic conidia arc probably unable to retain 
their vitality for a considerable period of time, and therefore may 
not be of great consequence in initiating the disease the following 
season. Some believe, however, that the scabby spots upon old 
fruits remain living, at least so far as the mycelium is concerned, 
and that new conidia may be produced the following spring. 
They would believe that this is particularly true when the fungus 
has attacked young twigs, and that therefore it is in favorable con- 
dition for early infection. Nevertheless, the fungus has not been 
found constantly or abundantly upon young twigs and it is quite 
probable that twig infections are less common than is supposed. 
In that case, the constant reappearance of the disease may be 
more generally due to the development of the perfect stage 
during the winter. 

So far as the development of the perithecial form has been 
followed in this country, it is believed that the first evidences of 
the perithecium in the case of the apple scab are found in October 
and later, the perithecia reaching maturity by April perhaps. At 
any rate, mature ascospores have been found during April and 
May, and the perithecia disappear by the following month. The 
perithecia are usually found on the under surfaces of the leaves, 
and Clinton believes that less conspicuous scabby spots develop 
the perfect stage most freely. The studies which have been made 
of the perithecia in artificial cultures, strengthened by the obser- 
vations in the open, seem to indicate beyond any question the 
relationships of these two forms. The perithecia are somewhat 
imbedded in the tissues of the leaf, are spherical or nearly 
spherical in form (Fig. 121), 90 to 150/A in diameter, and at 
maturity slightly beaked, these beaks being sometimes protected 
by half a dozen or more bristles. The perithecial wall is made up 
of cells more or less polygonal in outline. The asci are clavate to 
oblong or slightly curved, 55-75 X 6-i2/x. They are numerous in 
the perithecia and so far as noted there are no paraphyses. The 
spores are eight, becoming two-celled, one of which is larger than 
the other. The spores are olive-brown in color, 11- 15 x 5-7 M. 

The histological development of the perithecium has not been 
followed. The ascospores germinate readily in water, and some- 
times true appressoria are produced, as stated in the case of the 



270 



FUNGOUS DISEASES OF PLANTS 



germination of the conidia. The observation has been made 
(Chnton) that the scab is first seen more abundantly on the lower 
leaves, and from this the inference is drawn that infection is 
chiefly as a result of the production of the perfect or Venturia 
stage on old leaves which have fallen to the ground. The pro- 
duction of the perfect stage is common when the leaves fall upon 
sod and are more or less protected by their own number or by 
being partially covered with grass, etc. 




Fk;. 121. Ve.ntukia Pom/, from Wintered Leaves of Apple 

Control. In the agricultural experiment stations of the United 
States spraying experiments have been quite generally conducted 
looking toward the prevention of apple and pear scab. Some dif- 
ferences in treatment have been recommended for regions where 
climatic relations are diverse, but in general the method of treat- 
ment is much the same. At least one spraying should be made 
with strong Bordeaux mixture before blossoming. In California 
it has been recommended to spray twice before the fruit buds 
have opened ; this in case of the pear. A second (or third) 
spraying may be given immediately after the petals fall, and at 



ASCOMVCETES 27 1 

least one more two weeks after the second. The conditions, 
however, must determine the length of time intervening and the 
number of applications made. 

XLV. BITTER ROT OF THE APPLE AND OTHER FRUITS 
GlomereUa ntfomaciilans (Plerk.) Spaukl. (S: Von Sch. 

Blair. J. C. Bitter Rot of Apples. 111. Agl. Exp. .Sta. Built. 117: 4'^3-55i. 

1907. 
BuRRiLL, T. J. Bitter Rot of Apples. 111. Agl. Exp. .Sta. Built. 77 : 351-366. 

pi. C. 7?t,o\ 1-/2. 1902. 
BuRRiLL, T. J. Bitter Rot of Apples. 111. Agl. Exp. Sta. Built. 118 : 554-608. 

1907. 
Clinton, Ct. P. Bitter Rot. 111. Agl. Exp. Sta. Built. 69: 193-21 1. Ji^>-s. i-jg. 

1902. 
Clinton, G. P. Gnomoniopsis fructigena. 111. Agl. Exp. Sta. Built. 69 : 206- 

211. 1902. 
Edgerto.v, C. W. The Physiology and Development of Some Anthracnoses. 

Bot. Gaz. 45: 367-408. pi. 11. figs. 1-17. 1908. 
HAL.STED, B. D. Laboratory Studies of Fruit Decays. N. J. Agl. Exp. Sta. 

Rept. (1892): 326-330. 
ScHRENK, H. VON, and Spaulding, p. The Bitter Rot of Apples. U. S. Dept. 

Agl, Bureau of Plant Industry, Built. 44: 1-54. pis. i-g. 1903. 
(Consult this paper for more complete bibliography on the bitter rot.) 
Scott, W. M. The Control of Apple Bitter Rot. LI. S. Dept. Agl., Bureau 

of Plant Industry, Built. 93 : 1-33. pis. 1-8. 1906. 
Stoneman, Bertha. A Comparative Study of Some Anthracnoses. Bot. 

Gaz. 26: 69-120. pis. y-i8. 1898. (Gloeosporium fructigenum Berk. 

pp. 71-74- A^^- 1-4.33-3S, 83.) 

The most destructive apple disease in the chief apple-growing 
districts of the United States is unquestionably the bitter rot. 
This disease varies greatly in virulence with the conditions, 
becoming at times so destructive as practically to annihilate a 
crop in large areas. Fortunately, it does not appear in great 
quantity until midsummer, and then if the conditions are un- 
favorable it may not become a source of serious loss. 

Distribution. The bitter rot fungus is widely distributed in 
the United States east of and including Kansas, Oklahoma, and 
Texas. It seems to be particularly destructive in a more or less 
central area extending from the Atlantic seaboard in Virginia 
westward to Oklahoma. The fungus, however, is not limited to 
the United States, and is probably common and more or less 
injurious in all apple-producing countries. It is certainly known 



272 



FUNGOUS DISEASES OF PLANTS 



throughout Europe, AustraHa, and in some parts of Asia. The 
commercial relations between the different countries have doubt- 
less effected its very general distribution. In the United States 
it has been known for nearly half a century, although it is un- 
likely that it was a matter of commercial importance prior to the 
general and widespread development of orcharding, and the con- 
sequent more or less contiguous orchard areas. Certainly for 
twenty years it has been recognized as of serious economic 
importance in the central area already designated. 

Climatic relations. Evidences of the effects of the bitter rot 
fungus are usually found in July and August, although in the 
case of early summer apples in the far South, and under ex- 
ceptionably favorable conditions, it may appear much earlier. 
In common with most fungi, the favorable conditions are to 
be found in warm, sultry weather accompanied by rains, condi- 
tions so frequent during August in the chief bitter rot regions. 
During seasons thus characterized the fungus may spread with 
alarming rapidity, causing enormous devastation within a period 
of a single week, — this length of time being therefore sufficient 
under such circumstances for the propagation of the fungus 
probably through two or more generations. Von Schrenk states 
that the time of the appearance of the bitter rot is probably 
influenced by the following factors: (i) age of the fruits; (2) 
temperature and humidity of the air; (3) presence of spore- 
distributing centers. 71ie canker areas of the twigs are said to 
develop somewhat earlier in the season and under less restricted 
conditions. During cold, dry summers the apple is notably free 
from bitter rot, even though the fungus may have been un- 
usually common the previous season. Cold weather may act 
either as a preventive or as a check to the development of the 
disease after a favorable season for infection. 

Losses. It would be impossible to state the average loss sus- 
tained by the apple-growing industiy throughout the United 
States as a result of the ravages of this fungus. During years 
when the disease is prevalent the loss will certainly amount to 
millions of dollars. The president of the National Apple Grow- 
ers Association estimated the losses in 1900 at $10,000,000. 
l^urrill reported for the same year a loss in four counties in 



ASCOMYCETES 



■^iz 



Illinois amounting to $1,500,000. Apple growers have become 
so thoroughly informed as to the destruction of this disease that 
they have to a large extent adopted the remedies recommended 
as a result of recent investigations, and steps are now very 
generally taken to control this fungus. This general interest 
which has been awakened will doubtless tend to diminish losses 
in future years. 

Parts of the plant affected. Upon the apple the bitter rot 
fungus is active chiefly as a fruit parasite, although branches 
may also be affected. The first appearance of the fungus within 




Fig. 122. ]5itti;r Rot of Aptle 



the tissues of the fruit is made evident by a small brown spot 
beneath the skin. In the field, commonly, a single infection, or 
at most a few infections, are to be found upon one fruit. Under 
exceptionally favorable conditions, however, numerous infections 
may occur. In any case, the affected spot may increase rapidly 
in size, showing constantly a more or less circular outline with 
a well-defined margin. So soon as the spot has attained a size 
of one-fourth inch, more or less, the central portion of the 
affected area is sunken, and this is followed by the further 
gradual spread of the fungus throughout the fruit, and by the 
appearance of pustules as subsequently described (Fig. 122). The 
whole portion of the fruit affected by the fungus is decayed, and 



2 74 FUNGOUS DISEASES OF PLANTS 

the fruit near a decayed area is invariably bitter. This character, 
which appears to be quite constant, has given the disease its 
popular name. Affected fruits usually fall from the trees after 
a spot has attained considerable size. Nevertheless, in excep- 
tional cases the diseased fruits may hang on, and when the 
whole fruit has decayed as a direct or indirect effect of the fun- 
gus, they become dried, and to these fruits the term "mummy" 
has also been applied. 

The bitter rot fungus has been found upon various varieties 
of the apple. In some sections it is reported more commonly 
upon Ben Davis and Grimes Golden, but this may be more 
particularly due to the fact that these varieties were more gener- 
ally grown in the regions for which the report was made. The 
fungus is, in fact, notably unrestricted as to host. The apple 
is unquestionably the fruit most injured, yet the same fungus 
may be parasitic upon the grape, peach, pear, tomato, eggplant, 
and pepper ; at least, if infection experiments alone can be 
trusted to indicate what may take place in nature, the hosts 
above mentioned, as well as others, are all susceptible. 

The fungus. The life history of this fungus includes two 
stages, one an imperfect fungus, or properly gloeosporial stage, 
which is commonly produced upon the fruit, and the other 
an ascigerous stage, which may occasionally be produced upon 
a fruit or twig, and readily developed in artificial cultures.^ It is 
believed that the early infection of the fruit frequently arises from 
the development of pustules bearing conidia in canker areas, the 
spores falling from the canker areas to the fruit below. It has 
been frequently observed that affected fruits on a tree may map 
out a pyramidal area, at the cone of which may be found a 
cankered limb. Such canker areas (Fig. 123) apparently develop 
the conidia early in the season. The cankers are in the form 
of sunken areas upon twigs or limbs, and they are often round 
or oblong, sometimes several inches long, the bark covering such 
areas being cracked and broken. The bark readily dries out and 

1 As a result of his studies upon the fungus causing bitter rot Edgerton states : 
"' There are apparently two forms on the apple. These are separated in their geo- 
graphical distribution apparently by thermal lines ; the southern form differs from 
the northern considerably in cultural characters and it differs also slightly in the 
characteristics of the perithecium and the acervulus." 



1 



ASCOMYCETES 



275 



adheres closely to the underlying wood. Moreover, tlie develop- 
ment of a callus layer at the edge of the dead spot gives a further 
emphasis to the depression produced by the death and shrinking 
of the tissues within the canker spots. The canker spots are sup- 
posed to persist for at least two years. The mycelium of the fun- 
gus may be found in the inner bark and cambium. As previously 
suggested, the pustules of the fungus break through the bark in 
these cankered spots early in 
the season. 

When the fruit spots have 
attained a size of one fourth 
inch or more in diameter, 
there may appear in concen- 
tric lines small papillae, which 
are in reality the pustules of 
the fungus. The pustules are 
formed by the development of 
a stromatic mass of mycelium 
beneath the epidermis. From 
this stromatic mycelium there 
develops a cone-shaped mass 
of erect hyphae which eventu- 
ally rupture the cell walls. 
Meanwhile there are produced 
from the numerous, erect 
conidiophores an abundance 
of conidia. When the epider- 
mis is ruptured, these conidia emerge as a waxy, tendril-like strand, 
which may be at first pink in color, becoming gray with age. The 
spores are then imbedded in a gelatinous matrix readily soluble in 
water. Little may therefore be seen of the strand-like production 
of the spores during moist weather, or even during a period of 
heavy dews. Fig. 124 shows the relation of the conidiophores to 
the mycelial stroma. Examined microscopically the conidia are 
almost hyaline, though having a slight greenish cast. They vary 
in shape from ovate to oblong, or in some cases even slightly 
dumb-bell-shape. In general, however, they are ovoidal and vary 
greatly in size, according to the conditions under which they are 




Fig. 123. Canker uf the Bitter Rot 
Fungus. (Photograph by Perley Spaulding) 



276 



FUNGOUS DISEASES OF PLANTS 



produced. Some observers have recorded extreme sizes, 6-40 x 
3i-7yu,. More frequently, however (Von Schrenk), they are 12- 
16 X 4-6 /Lt. The conidia germinate readily, and upon germination 
almost invariably become septate. Under unfavorable conditions 
a germ tube may develop at its tip a brown resting cell termed a 
secondary conidium or appressorium. It is believed that the germ 
tube may obtain entrance to the fruit through the uninjured skin 
of the apple, and certainly artificial infection may result without 
noticeable surface injury. Nevertheless, infection can be hastened 
by injuring the surface, and it is possible that some slight injury or 
abrasion may be essential to penetration, although the belief is cur- 
rent that entrance may be effected through the stomates of the fruit. 




Fig. 124. Glomhrella rufomaculans:(Zo's\'d\\\. and Ascigerous Stages 

This imperfect form was for a long time the only known fruiting 
stage of the fungus. It was referred to the genus Gloeosporium 
and was generally known as Ghvosporiiim fructigcjimn Berk. 

The perithecial stage of this fungus, found by Clinton in 1902, 
may be readily developed in artificial culture, though Clinton has 
also reported having found it frequently upon the fruit. In cul- 
tures it may be developed within two weeks on various nutrient 
media, while in nature it develops apparently only the following 
spring upon fruit which has been upon the ground throughout the 
winter. In artificial culture the perfect stage develops promptly 
and vigorously upon apple agar corn meal. The mycelium first 
forms small black nodules which become stromatic cushions about 
one fourth inch in diameter. Within this stroma one or many peri- 
thecia might be developed. The various stages in the development 



ASCOMVCETES 



277 



of the perithecium have not been very carefully followed, although 
it would appear that the formation of asci in the perithecium is pre- 
ceded by a central mass of hyaline cells, which are displaced as 
the asci arise. At maturity the asci are oblong-clavate, 55-70 x 9/a. 
Each ascus contains eight spores, frequently arranged in pairs, 
though sometimes in oblique series. The ascospores are curved, 
but in general resemble the conidia. They are, however, more uni- 
form in size, being usually 12-22 x 31^-5 //■. The asci are evanes- 
cent, and the ascospores germinate without a period of rest. 

It is not believed that the ascus-bearing stage is at all essential 
to the annual appearance of this disease. It has been frequently 
shown that the conidia in mummied apples retain their vitality 
until the following season, and it is probable that infection could 
result from conidia produced on apples which have remained on 
the ground throughout the winter. However, when all mummied 
fruits in the trees as well as under the trees have been carefully 
destroyed, the disease has been found abundantly the following 
season. It is therefore probable that a great many infections re- 
sult through canker spots formed during the summer. These live 
over winter and produce conidia again during the early summer. 

Cultural relations. This fungus may be readily cultivated in 
the laboratory on almost any of the ordinary nutrient media. 
Apple agar is especially favorable, but, as already indicated, apple 
corn meal agar is perhaps as good as any other medium for the 
production of the ascosporic stage. The conidia germinate within 
a few hours and the mycelium grows with great rapidity. The 
mycelium is septate, and neighboring cells of different mycelia 
readily fuse. In the tissues of the apple the hyphae are brown 
with age. In culture, however, the hyphae are at first only 
slightly colored. The conidia are produced in quantity in culture, 
appearing upon an agar plate within twelve hours. Under such 
conditions the conidia are generally borne upon numerous lateral 
branches. Upon sterilized fruit in the laboratory the production 
of conidia within the pustules has required, under the most favor- 
able conditions, only forty-eight hours. It is evident therefore 
that in the field many generations of this fungus may be pro- 
duced within a very short time, and that its rapid spread is well 
explained by the brief period required for spore production. 



278 FUNGOUS DISEASES OF PLANTS 

Control. It is of unquestionable value to keep the orchard as 
clean as possible of apples affected with the bitter rot fungus, 
and it is likewise important to prune out all cankered limbs. 
Nevertheless, these precautions alone are wholly insufficient, and 
it has recently been demonstrated that the disease may be con- 
trolled — at least under the conditions prevailing in the eastern 
United States — by a proper application of Bordeaux mixture. 
Under conditions favorable for the spread of the disease, from 
93.3 to 98.9 per cent of sound fruit has been harvested upon 
sprayed trees, while the controls gave practically no fruit of value. 
It is recommended to make about four applications of Bordeaux 
mixture, although one or two additional applications may be 
necessary. In this as in all other such work, the tree should be 
thoroughly sprayed from a nozzle giving a mist-like application. 
When spraying for bitter rot alone the first application may be 
made about forty days after the petals have fallen, subsequent 
applications being given about two weeks apart. During very wet 
weather, however, greater frequency may be required, while in 
cool weather the length of time may be increased. Beneficial 
results from spraying experiments have also been obtained in the 
central West, and it is believed that there the disease may be 
controlled by the methods suggested. 

XLVI. ANTHRACNOSE OF SYCAMORE 
Gnoino7iia Veneta (Sacc. & Speg.) Kleb. 

Edgerton, C. W. The Physiology and Development of Some Anthracnoses. 
Dot. Gaz. 45: 367-408. pi. 11. Jigs. 1-17. 1908. 

Klebahn, H. Unters. iiber einige Fungi imperfecti u. d. zugehorigen As- 
comycetenformen. Jahrb. f. wiss. Bot. 41 : 515-558- 1905- 

ScRiBXER, F. L. A Disease of the Sycamore. U. S. Dept. Agl. Rept. (1888): 
387-389. pi. IS. 

SouTHWORTH, E. A. Gloeosporium nervisequum (Fckl.) Sacc. Journal My- 
cology 5 : 51-52. 1889. 

Habitat relations. This fungus is parasitic upon the leaves 
and young shoots of the sycamore or plane tree, Platamts 
occidentalism and it is widely distributed in Europe and America. 
In one or more stages the fungus also appears to produce spots 
upon the leaves of several species of oak, being reported upon 
Qiiercits alba, Qtierciis veluti)ia, and Querents coccinea. Upon 



ASCOMYCETES 



279 



the sycamore it is in one stage primarily a disease of the leaf 
veins, although commonly the death of considerable portions of 
the lamina adjacent soon follows. In another stage the fungus 
is notably fatal to shoots, young trees, and seedlings. According 
to Edgerton this fungus may produce in the early spring an 
effect very similar to frost injury. Indeed, these injuries have 
been referred by several to spring frosts. (3n the whole this is 
one of the most disastrous anthracnose diseases known, and far 
greater attention would be directed to it if greater concern were 
felt for the sycamore, which is, nevertheless, a most important 
shade tree. 

The fungus. The interesting life history of this fungus has 
been carefully worked out. There are three types of imperfect 
fungi as well as the ascigerous form in the life cycle of this organ- 
ism. A typical Gloeosporium stage {see Gloeosporium) appears 
upon the leaves, and the pustules or acervuli are well developed 
upon the veins of both the upper and lower surfaces. Upon 
small, colorless conidiophores ovate conidia are produced measur- 
ing 10-15 X 4-6 /u,. The acervuli are from 100 to 300 /i in diam- 
eter, and the spores are produced in such quantity that in moist 
weather they are forcibly ejected in creamy masses or strings. 
This stage has long been known to mycologists as Glaospoi-hivi 
jicn'iscqii?iin. Upon the twigs the size and type of acervulus has 
caused the fungus to be referred to the form genus Myxosporium. 
The further growth of the stroma later in the season may develop 
the pycnidial or Sporonema stage, in which similar small conidio- 
phores are developed from all sides of a more or less chambered 
pycnidium. The ascigerous stage is abundantly developed on 
affected leaves which have wintered over in the open. This stage 
may appear either during late winter or early spring. The peri- 
thecia vary greatly in size, but are ordinarily from 150 to 250//. 
in diameter, with beak 50- 100 /a long. The asci are, according to 
Edgerton, 48-60 x 12-15 /a. They are broadly clavate and bent 
at right angles near the base. The apex is thickened, and there 
is a terminal pore surrounded by a more refractive ring. The 
ascospores are invariably eight; they are hyaline, elliptical or 
arcuate, once septate, and composed of a large upper cell and 
a small lower. The germ tube emerges invariably from the larger 



28o FUNGOUS DISEASES OF PLANTS 

cell. The various spore forms of this fungus have yielded in cul- 
ture a perfectly similar mycelium, and infection experiments seem 
to leave no doubt as to the genetic relationship. 

Control. Preventive measures might at least apply to nursery 
stock and to young trees recently set. It may be supposed that 
thorough applications of the 5-5-50 Bordeaux very early in the 
season would greatly assist in the control of this disease. 

XLVII. A DISEASE OF YOUNG OAKS 

RoscUinia Qucirina Hartig 

Hartig, Robt. Die Eichenwurzeltodter. Unters. a. d. forst.-bot. Inst. Miin- 
chen(i88o): 1-32. p/s. 1,2. 

This fungus occurs as a parasite of seedlings and young oak 
trees in Germany.^ It affects primarily the roots and the basal 
portion of the stem. It has been prevalent in northwestern 
Germany and particularly disastrous when it occurs in the seed 
beds. The greater amount of injury results to seedlings from one 
to three years old. The effects of the fungus are manifest by an 
unhealthy, pale color of the foliage, followed by withering and 
wilting of the leaves. Young shoots, and subsequently the older 
leaves, also wither and die. About the roots and sometimes the 
lower portion of the stem will be found a felt-like mycelium of 
interwoven brown threads, or strand-like aggregations. 

The perithecia are commonly produced in quantity, particularly 
after the death of the plant. They are spherical or ovate in form, 
and brittle in texture, with a papillate ostiolum. The asci are long- 
cylindrical, each containing eight elliptical or somewhat fusiform, 
brown or brown-black spores, which are ordinarily vacuolate, and 
measure 28 x 6-//*. 

1 One or two other species of Rosellinia have been described as important 
from the disease point of view. Prillieux (Comp. Rend. 135 : 275. 1902) found 
a form on the roots of fruit trees accompanying Dematophora, which he considers 
to be the perfect stage of the latter. lie believed that the perithecia were developed 
on the stroma on which arose the conidiophores. The perithecia measure 1.5 mm. 
in diameter, are gray-brown in color, with a definite and darker papilla. The body 
is composed of three wall layers, — the outer indurated and brown, the central 
white, and the inner yellowish in color. From the latter arise the stalked asci, 
365-380 X 8.5-9/x, and small slender paraphyses. The spores long remain color- 
less, but are finally black with small vacuoles. 



I 



ASCOMYCETES 28 1 

XLVIII. BARK DISEASE OF CHESTNUT 
Diaport/ic f^arasitica Murrill 

Metcalf, Haven. The Immunity of the Japanese Chestnut to the Bark 
Disease. Bur. Plant Ind., U. S. Dept. Agl. Built. 121: 55-56. 1908. 

Murrill, W. A. A Serious Chestnut Disease. Jour. N. Y. Bot. Garden 7: 
143-153- figs- I3'i9- 1906. (Also 7: zo-},-z\\. Jigs. 25-30. 1906.) 

Murrill, W. A. A New Chestnut Disease. Torreya 6 : 186-189. fig. 2. 
1906. 

Occurrence. This bark di.sease of the chestnut has recently 
been reported from New York, New England, and other north- 
eastern states, and it would appear that it is spreading rapidly. 
It is in fact becoming a serious menace to forest tree culture in 
that section of the country. The common species of chestnut 
{Castanca dcntata), seems to be in all localities peculiarly sus- 
ceptible, and so far as the observations go, all species of the 
genus Castanea are subject to it with one exception, this excep- 
tion being certain Japanese varieties of Castanca cirnata Sieb. 
and Zucc. Metcalf has found the latter to be quite generally 
immune, and while the nuts are inferior in flavor to the best 
European varieties, it is nevertheless an important commercial 
product. It is hoped that hybridization between the Japanese and 
American or European forms will be successful in establishing 
immune varieties with other desirable characteristics of the better 
sorts. It is not believed, however, that the Japanese chestnut 
can to any extent replace the native tree for forest purposes, 
although the former is desirable from an ornamental standpoint. 
It is suggested that since the Japanese chestnut was first intro- 
duced on Long Island, it is possible that Japan may be the home 
of this fungous pest, and that as a result no resistance could have 
been developed in the native species. 

The fungus. The fungus has been found upon twigs, small- 
sized branches, and trunks. It completely encircles the affected 
limbs, and the girdling thus brought about ultimately causes the 
death of portions beyond, and lessened vitality of the whole tree. 

The mycelium of the fungus is confined very largely to the 
bark and to the underlying cambium. The affected cortex be- 
comes somewhat light brown in color and slightly sunken after 
desiccation. 



282 FUNGOUS DISEASES OF PLANTS 

Infection does not seem to be possible through uninjured 
outer bark, but when the latter is punctured or broken, the 
fungus promptly penetrates the living tissues. It is inferred, 
therefore, that infection occurs through wounds and possibly 
through lenticels. 

During the summer there is developed through the lenticels 
from a stromatic mycelium the imperfect stage of the fungus. 
This latter produces small, rod-like but curved spores, character- 
istic of the genus Cytospora of the imperfect fungi. These spores 
are discharged in long, twisted, brownish, thread-like masses. This 
stage serves for the very rapid propagation of the disease. 

During autumn there may be produced from the stroma in the 
inner bark the perithecial stage. The latter appear in clusters of 
from ten to twenty. They are flask-shaped with long, slender 
necks protruding above the surface. The asci are, according to 
Murrill, 45-50 x 9/i. They are constantly eight-spored, hyaline, 
oblong, two-celled, and measure 9-10 x 4-5/"'. 

Control. No practical method of controlling this fungus has 
been suggested. Severe pruning is certainly advisable if the dis- 
ease is detected when twigs or branches alone are infested, and it 
is possible that systematic effort may hold the disease in check, 
even where the conditions are favorable for its spread. Spraying 
is perhaps impracticable. 

XLIX. BLISTER CANKER OF APPLE 

Nummularia discreta Tul. 

Hasselbring, H. Canker of Apple Trees. 111. Agl. Exp. Sta. Built. 70 : 225- 
239. ph. 1-4. 1902. 

The blister canker of the apple is well distributed throughout 
the apple-growing region of the Mississippi Valley, and doubtless 
in other sections of the United States. It also occurs in Europe, 
but has not been reported as a disease worthy of special consider- 
ation. This canker, like others already described, is, however, a 
source of constant danger on account of the fact that it is per- 
ennial in the host and in time is sure to cause the death of large 
limbs or of the entire tree. The blister canker has been termed 
the Illinois canker, since it was first observed as particularly 



ASCOMYCETES 



283 



destructive in that state. Under ordinary circumstances the fungus 
is doubtless a mere saprophyte, and it is not restricted to the apple 
or to other members of the apple family. It has in fact been found 
upon such trees as the following : American elm {LJlnins americana). 
Magnolia sp., Judas tree {Ccrcis canadensis), and Sorbns sp. 

Symptoms. The disease is usually found upon the larger limbs 
or upon the trunk, and the appearance of the canker areas is so 
characteristic that it cannot be 
mistaken, at least in late stages 
of the disease, from any of the 
cankers thus far discussed. 
At first the infested areas are 
brown, slightly sunken, and con- 
sist of small spots of healthy 
tissue intermingled within the 
general diseased area. These die 
later, but there is an irregular 
and mottled effect which per- 
sists and is readily observed. 
The infected area may cover 
many square inches of surface, 
and it is sharply delimited from 
the healthy tissue, due to the 
drying and cracking. Occa- 
sionally there is a slight de- 
velopment of slime during the 
early part of the season, but 
this has not been associated witli the action of the parasite. 

Hasselbring describes the external appearance during the late 
season as follows : 

The bark of the older parts becomes much roughened and blackened as if 
it had been charred. Numerous rifts and cracks appear over the surface of the 
dead bark, which is very dry and brittle, and falls off in irregular patches, ex- 
posing the dead wood. The circular stromata are firmly attached to the wood 
by means of a ring of hard fungous tissue, so that they remain seated on the 
wood even after the bark has fallen away. The entire blackened area is dotted 
over with the circular stromata, which form the most pronounced distinguishing 
feature of this canker. The disease is always easily recognized by these stromata 
(Fig. 125), which distinguish it clearly from the New York apple tree canker. 




Fig. 125. Bt.ister Canker of Attle 



284 



FUNGOUS DISEASES OF PLANTS 




The fungus. The mycelium penetrates the bark and later the 
wood beneath to a considerable extent. The course of the fungus 
through the bark and wood is very largely through the paren- 
chymatous and medullary cells. From these, however, it infests 
neighboring tissues, especially the xylem vessels. The stromata 
and fruit bodies are developed from the latter part of the summer 
into the autumn and winter. From the upper surface of the 
stroma a mat of conidial hyphas arises. These break through the 

epidermis and underlying fun- 
gous tissue. The conidia are 
simple, hyaline spores which 
apparently do not readily ger- 
minate. Later in the season 
the underlying stromatic tis- 
sue which is now cup-shaped 
shows the development of 
flask-shaped perithecia sunken 
in that portion of the stroma 
which is made up chiefly of 
fungous tissue. Bordering the 
stroma a black line of more 
abundant fungous tissue is 
also evident. The body of the 
perithecium is elliptical or 
ovate at maturity, and it is com- 
pletely filled with long-cylin- 
drical asci about 160 x 13 /a. 
The asci are thick-walled with 
terminal pore, and contain at maturity eight more or less spher- 
ical, brown spores. The latter often measure 13 x lO/i, and a clear 
space along one side indicates the line of rupture during germina- 
tion. Twin germ tubes are invariably developed. 

Control. Observations on the progress of this disease would 
seem to indicate that this fungus gains entrance through wounds, 
and prevention consists in avoiding as far as possible the im- 
proper injuries due to careless methods of pruning, cultivation, 
and harvesting. Moreover, the cankered areas on limbs should 
be pruned out and destroyed when found. 




Fig. 126. A^UMMULARIA DISCRETA : THE 

Blister Canker Fungus 
rt, stroma ; b, perithecium ; c, ascus 



CHAPTER XII 

FUNGI IMPERFECTI 

The imperfect fungi, or fungi imperfecti, constitute an heter- 
ogeneous subdivision of the true fungi. As a class it is not com- 
parable to the natural classes thus far discussed, yet it may be 
given an equivalent name and regarded as a coordinate division 
for the sake of convenience in general treatment and classifica- 
tion. The fungi thus brought together consist of species hav- 
ing hyphomycetous, melanconiaceous, or sphaeropsidaceous types 
of spore production. Since these types may represent special 
" stages " in the life cycles of other fungi, these secondary fruit 
forms in general will not permit of certain classification under the 
groups thus far discussed, much less under the Basidiomycetes 
subsequently treated. The great majority, however, and perhaps 
all of those here discussed would unquestionably find their natural 
relationships with various genera of the Ascomycetes, and for that 
reason they are conveniently treated as following that group. 
Some of the Hyphomycetes in general, however, might represent 
imperfect forms of the Phycomycetes or even of the Basidio- 
mycetes. In any case it would generally be impossible to de- 
termine the genus or even the family in which a particular 
imperfect fungus or form genus might be placed. It is therefore 
essential to have such form genera, under which species may be 
described and classified until their complete life cycles are known, 
when they may be transferred to the proper natural genus (genus 
of so-called perfect fungi). In many other minor ways the form 
genus is a matter of convenience and certainly contributes some 
stimulus for a better description of the different spore forms in 
the polymorphic species. 

Among the imperfect fungi, as here interpreted, three chief 
subdivisions are generally recognized, as follows : 

HypJwniycctes — conidia borne upon exposed conidiophores 
which may be single, fascicled, or united together in a columnar 
or tubercular fashion. 

285 



286 FUNGOUS DISEASES OF PLANTS 



^ 



Melanconialcs — conidia borne on relatively short conidiophores 
arising from or within a more or less differentiated stroma, pro- 
duced usually beneath the epidermis. 

Sphceropsidales — conidia borne on short conidiophores arising 
within a perithecium, or pycnidium, or sometimes within cavities 
of a dense stroma. 

The primary subdivisions of these groups are termed families, 
and in the case of the Sphaeropsidales this classification is based 
on characters more or less comparable to those separating certain 
orders or families of the Ascomycetes. The secondary and further 
subdivisions down to the genera are properly an artificial classifi- 
cation based chiefly upon the color of the spores and the extent 
of septation. Details of this classification may be found in the 
taxonomic works ; but a brief comparison of important genera 
embracing parasitic species is here included. 

I. HYPHOMYCETES 

I. {Muccdincc^ ; mycelium and spores generally light colored.) 

Oospora. In this genus the vegetative mycelium is delicate and 
inconspicuous. The conidia are relatively numerous, ovoidal to 
spherical in form, hyaline, and unicellular (amerosporic). 

Monilia. In this case the vegetative hyphas are more evident 
and the fertile hyphse are branched, often in dense clusters, with 
hyaline or slightly colored conidia produced in chains. To this 
form genus the conidial stage of the brown rot of stone fruits 
may be referred (cf, Sclerotinia fructigend). 

Oidium. As generally interpreted this genus includes among its 
representatives the conidial stage of Erysiphaceae (cf. page 215). 
The powdery mildew of the vine was long known only as Oiduini 
Tuckcri. The conidia are produced in chains on short, erect 
hyphae generally arising from a superficial mycelium, 

Sporotrichum possesses an extensive mycelium and conidio- 
phores which are, as a rule, well differentiated. The latter are 
branched and bear numerous, hyaline, one-celled, more or less 
spherical conidia. These originate from tips of branches or on 
minute sterigmata. Some species of this genus parasitic or sapro- 
phytic upon insects are connected with a compound form, Isaria, 
and an ascigerous stage, Cordyceps. 



FUNGI IMPERFECTI 287 

Botrytis. This genus, although somewhat indefinitely character- 
ized, differs from the preceding chiefly in having spores grouped 
at the tips of branches and ordinarily borne on papillae or tooth- 
like projections. 

Cephalothecium is characterized by relatively long, unbranched, 
upright conidiophores, at the tip of each of which may be produced 
a cluster of two-celled, hyaline (hyalodidymic), usually pear-shaped 
conidia. 

Ramularia. The mycelium is wholly within the tissues of the 
host, the conidiophores are hyaline, straight or flexuous, single or 
fascicled. The conidia are single or loosely adherent in chains. 
They are narrowly elliptical to cylindrical, and divided into three 
or more cells (hyalophragmic). 

Cercosporella. This genus is related to the preceding on 
account of its hyaline conidiophores and conidia, but on the 
other hand it is very close to Cercospora, subsequently described, 
on account of the filiform spores (scolecosporic) and sometimes 
geniculate conidiophores. 

Piricularia differs from the preceding genus in having conidia 
which are strongly obclavate to pyriform and generally pluriseptate. 

2 . {Dcmaticae ; mycelium dark, at least with age ; spores 
generally dark.) 

Fusicladium. The mycelium produces short conidiophores 
which may be single or in small clusters. These produce at 
the tips elliptical conidia which at maturity are two-celled and 
colored (phseodidymic) (cf. Venturia, page 264). 

Polythrincium differs from the last-mentioned genus chiefly in 
the nodulose or twisted conidiophores. 

Scolecotrichum. These forms possess, instead of nodulose 
conidiophores, those which are geniculate, a knee being formed 
as the conidiophore is prolonged by growth on one side of each 
spore successively produced. The spores are more or less ellip- 
tical and two-celled. 

Cladosporium. In this genus there is less regularity in the 
form of the conidiophores and the sizes of spores, as the conidio- 
phores are considerably branched, and these branches may be- 
come spores. The conidiophores are olivaceous, also the ovate, 
eventually two-celled conidia. 



288 FUNGOUS DISEASES OF PLANTS 

Helminthosporium possesses straight, dark colored conidio- 
phores bearing club-shaped or spindle-form, many-celled, flavous 
to dark colored conidia (phaeophragmic). 

Macrosporium. In this genus the straight conidiophores bear 
ovoidal or elliptical spores which are transversely septate, and 
many of the cells thus formed become longitudinally, and then 
even again transversely, divided (dictyosporic). 

Alternaria differs from the previous genus particularly in hav- 
ing the conidia borne in chains, and these conidia are often 
clavate in form. 

Cercospora possesses straight, flexuous, or strongly geniculate 
conidiophores, which may be single or grouped. The conidia 
are needle-shaped or filiform (scolecosporic), hyaline to considera- 
bly colored, and from three to many times septate. This is one 
of the largest genera of the Hyphomycetes, containing about five 
hundred described species, more than three fourths of which are 
attributed to North America. All species are parasitic. 

3. {Tnbo'cnlarice ; conidiophores in the form of a tuberculate 
mass, or sporodochium). 

Volutella. In this genus the sporodochium, or fruiting tubercle, 
is a more or less closed, disciform body, not, however, produced 
on a basal stroma. It is provided, around the border, with hair- 
like setae. The conidiophores are mostly unbranched and give 
rise terminally to hyaline, unicellular conidia. 

Fusarium. In this genus the sporodochia are small cushion- 
like masses of interwoven hyphse which may appear waxy or fila- 
mentous in texture. The conidiophores proper are unbranched, 
and they bear successively at the tips curved or sickle-shaped, 
hyaline, many-celled (at maturity) conidia, 

II. MELANCONIALES 

Gloeosporium. The spore-producing pustule, or acervulus, may 
be extensive, and is made up of a mass of relatively short conidio- 
phores arising from, and commonly partially inclosed within, a 
stromatic cushion of fungous tissue. At maturity the stroma 
opens, and thus it ruptures the epidermis. It may even expand 
so widely as to seem to constitute merely a basal stroma. The 
spores are ovoidal, fusiform, or slightly curved, and hyaline 



\ 



FUNGI IMPERFECTI 289 

(hyalosporic). There arc supposedly about three hundred species, all 
of which are parasitic. Some species are connected with Glomerella 
or related genera (cf. Glomerella rnfomaeulatis, page 271). 

Colletotrichum, including about forty species, has characters 
similar to the preceding except that the acervlili are bordered by 
from few to many dark, rigid setae, usually several times the 
length of the conidiophores. 

Marssonia is a genus similar in development to Gloeosporium 
except that it possesses, as a rule, less extensive acervuli, two- 
celled (hyalodidymic) spores, and it occurs on leaves only. 

Septogloeum is another genus of the Gloeosporium type except 
that the long-elliptical or cylindrical conidia are pluriseptate. 

Coryneum is characterized by simple conidiophores and dark, 
triseptate or pluriseptate conidia (phaeophragmic) without append- 
ages of any kind. The conidia are not set free in horn-like or 
tendril-like masses. 

Pestalozzia is readily distinguished by the peculiar conidia, 
which are more or less elliptical, triseptate or pluriseptate, the 
apical and basal cells being hyaline or very light colored, and the 
central cells dark. The apical cell is provided with one or more 
filiform appendages. The conidiophores are also filiform. 

Cylindrosporium is comparable to Septoglceum except that the 
spores are filiform or needle-shaped, usually curved and continuous. 

III. SPH/EROPSIDALES 

Phoma. In members of this genus the pycnidia are single, or 
sometimes closely aggregated. They are immersed in the tissues 
of the host until maturity, when the epidermis is ruptured. The 
conidia are small, hyaline, usually ovate or elliptical, and continu- 
ous. The genus is arbitrarily limited to those species having 
spores less than 1 5 yu,, larger forms being relegated to Macro- 
phoma. Species of Phoma inhabit fruits, twigs, or, in some 
cases, all parts of the hosts, but they are considered to produce 
no definite spots. About eleven hundred species of this genus 
are recognized, but relatively few of these have been determined 
by broad comparison or careful cultural studies. 

Phyllosticta applies to species similar, morphologically, to those 
in the preceding genus. Phyllosticta, however, produces definite 



290 FUNGOUS DISEASES OF PLANTS 

spots and inhabits leaves only. This is also a very large genus, 
consisting of about eight hundred species. 

Forms of both Phyllosticta and Phoma, occurring on the grape, 
have been found to be stages of a Guignardia. Some species of 
Phoma would seeni to be imperfect stages of Diaporthe, and 
others have been associated with still other ascigerous forms. 

Sphaeropsis includes species with relatively large, continuous, 
colored conidia (phaeosporic). The conidia are generally elliptical. 
The pycnidia are at first immersed and finally break through the 
epidermis. They are black with papillate ostiolum. There are 
nearly two hundred species of this genus, of which a few are 
important parasites. 

Coniothyrium, which includes nearly as many species as 
Sphaeropsis, differs from the latter chiefly in the smaller size of 
the spores, which, moreover, are often less colored. 

Septoria. In this genus the pycnidium resembles closely that 
of Phyllosticta or Sphaeropsis, but the spores are long and fili- 
form, often slightly curved, usually pluriseptate. With respect to 
spore characters, therefore, the genus corresponds more or less 
to Cercosporella and Cylindrosporium of the imperfect fungi 
here described. 

Leptothyrium is characterized by a more or less superficial, 
shield-shaped, black pycnidium without definite ostiolum. The 
spores are one-celled and hyaline. 

Entomosporium possesses relatively large, black pycnidia with- 
out ostiola. The spores are four-celled in the form of a cross, the 
horizontal cells smaller. Each cell is provided with a delicate awn- 
like appendage. 

IV. POTATO SCAB 

Oospora scabies Tliaxter 

Sturgis, W. C. On the Susceptibility of Various Root Crops to Potato Scab, 
etc. Conn. (N. H.) Agl. Exp. Sta. Rept. 20: 263-266. 

Thaxter, Roland. The Potato "Scab." Conn. Agl. Exp. Sta. (1890): 
81-95. 

Thaxter, Roland. The Potato Scab. Conn. Agl. Exp. Sta. (1S91): 153-160. 

The scab of potatoes is a disease which is well known to grow- 
ers, dealers, and consumers alike, for the conspicuous scab pits or 
spots on the surface of tubers cannot fail to strike the attention. 



1 



A 



FUNGI IMPERFECTI 29 1 

The disease is most common throughout the United States, and 
doubtless throughout the potato-producing regions of Europe as 
well. It is not positively demonstrated, however, that all of the 
surface injuries known as scab are properly referable to the fungus 
here discussed as the causal organism, yet it is highly probable that 
potato scab as a common disease is generally due to Oospora scabies. 
Sturgis and others have found turnips {Brassica catnpestris), 
beets, and mangels {Beta -c'ulgaj-is) susceptible to this disease. Car- 
rots {Danciis Carota) and parsnips {Pastinaca sativa) are not re- 
garded as susceptible. It is possible, moreover, that this fungus 




Fig. 127. Potato Scab 

may occur upon the less conspicuous roots of some other plants, 
but it is typically a disease of fleshy roots. 

Before the scab organism had been isolated and careful inocu- 
lation experiments made, a great variety of causes were assigned 
by observers and investigators, various bacteria and fungi, also 
insects and myriapods being held responsible for these injuries. 

The result of Thaxter's studies in 1 890 furnished proof that the 
common form of scab in New England is caused by a minute par- 
asitic fungus tentatively designated as above. The disease ^ " first 
shows itself as a minute reddish or brownish spot on the surface 

1 Thaxter, /. c, 1890. 



292 



FUNGOUS DISEASES OF PLANTS 



1 



of the tuber, often making its appearance when the tuber is very 
young, and sometimes not until it has reached a considerable size. 
This discoloration very commonly, though not invariably, has its 
origin in one of the roughened points, or lenticels, which are scat- 
tered over the surface of the potato, and after it has once appeared 
may extend quite rapidly to the adjacent tissue, becoming deeper 

in color and being associated 
with an abnormal corky de- 
velopment of the parts in- 
volved, which often cover a 
considerable area. This area 
may constitute a more or less 
irregular scab-like crust over 
the surface, or more fre- 
quently may become deeply 
cracked and furrowed, the 
depth and extent of the injury 
depending in a great meas- 
ure upon the stage at which 
the tuber first became dis- 
eased ; those which are at- 
tacked while very young 
showing, as might be ex- 
pected, by far the most deep 
seated injury" (Fig. 127). 

If scabby potatoes are 
carefully harvested and im- 
mediately examined, there 
will be found associated with 
the disease an evanescent 
grayish film. This film is made up of extremely delicate, minute, 
refractive, branched filaments, which break up into bacterioidal 
cells. Some branches are curved, and spore-like structures are 
also produced within certain cells. 

Experiments demonstrate that the fungus may persist in the soil 
several years. A few scabby potatoes are sufficient to spread the 
organism to a bin of clean tubers. To secure potatoes free of scab, 
clean tubei\s should be planted in soil free from the fungus. 




Fig. 1 28. A Sugar Beet affected with 
Scab 



FUNGI IMPERFECT! 293 

Control. Abundant experimental work lias shown that of the 
two possible lines of control, soil treatment or seed treatment, the 
latter is most effective ; and this, together with a judicious rota- 
tion of crops, is sufificient permanently to control this disease. 
The method of treating the seed tubers consists in immersing 
them for two or more hours in a solution of i ounce of formalin 
to every 2 gallons of water, or in a solution of bichloride of mer- 
cury, consisting of i ounce to 8 gallons of water. 



V. BUD ROT OF CARNATIONS 
Sporotrichuui Poce Pk. 

Heald, F. D. The Bud Rot of Carnations. Neb. Agl. Exp. Sta. Built. 103 : 

pis. 1-8. 1908. 
Stewart, F. C, and Hodgkiss, H. E. The Bud Rot of Carnations and the 

Silver Top of June Grass. N. Y. (Geneva) Agl. Exp. Sta., Tech. Built. 

7: 83-119. pis. 1-6. 1908. 

Habitat relations. The bud rot of carnations has recently 
received careful attention as of importance in some of the green- 
houses of New York, Illinois, and Nebraska. In cases where the 
infection is late in developing, or where the conditions are un- 
favorable for the fungus, the infected flowers may be only slightly 
abnormal or disfigured. Even in these cases, however, the petals 
become eventually discolored, and the death of the calyx also en- 
sues. In severe attacks, or under favorable conditions for the 
fungus, there is developed within the bud a soft rot. resulting 
in discoloration of all the parts. Occasionally the evidences of 
fungous growth are sensible to the unaided eye. 

Commonly there is associated with the fungus a species of 
mite. According to the experimental evidence, this mite has no 
causal connection with the disease, but it is doubtless of im- 
portance in the distribution of the fungus. In an early stage 
of the attack, the mites are extremely minute, and might be over- 
looked ; but later the distention of the mite body makes it an 
object of such size that it may not be overlooked even upon 
casual observation. Experiments have clearly indicated that the 
fungus is able to produce the disease when inoculated in the 
young buds by needle prick or scalpel wound. 



294 



FUNGOUS DISEASES OF PLANTS 



The fungus has been isolated and can be readily grown in 
artificial media. Upon starchy media, or media containing con- 
siderable sugar, it produces a very vigorous growth, often cottony 
in appearance. Glucose agar, corn meal, etc., are colored pink, 
or some shade of deep red after growth of a week or more ; but 
the color is less intense when the fungus is grown on starchy 
products, apparently, than on a glucose agar. 

The fungus. It produces two forms of conidia, which have 
been designated microconidia and macroconidia (Fig. 129). The 
microconidia are more or less subspherical, or slightly pointed at 
the base, even pear-shaped, and they are produced by a constric- 
tion from lateral or 
terminal branches, the 
latter being sometimes 
clustered. Each branch 
may produce a large 
number of conidia by 
successive abscision, 
and the conidia fre- 
quently become massed 
together in balls. They 
vary from 5.5 to 8/z 
in diameter, and are 
capable of immediate 
germination, producing a much branched mycelium. The macro- 
conidia are far less frequent in culture and in nature than the 
microconidia. The method of production of the former type is 
practically the same as in the case of the microconidia. There is, 
however, greater vacuolation of the protoplasmic contents during 
the formation of the macroconidia, which, moreover, may become 
ovoidal, and finally further elongate, becoming once or more septate. 
They measure 4.5-5.8 x 10-17. 5 /u.. Owing to the fact that the 
conidia are in general microconidia, properly the type of the genus 
Sporotrichum, this fungus is retained in that genus. 

Control. This disease is often one of serious importance in 
well-arranged and sanitary carnation houses ; but it is apparently 
most to be feared where conditions for forcing the host are desired, 
or where unsanitary conditions prevail. Control or prevention 




Fig. 129. Sporotrichum PoAi : Cunidioph(jres 
AND Conidia 



FUNGI IMPERFKCTI 



295 



therefore concerns itself primarily with a maintenance of condi- 
tions as dry and cool as is compatible with satisfactory growth, 
and also with matters of general sanitation, such as proper ven- 
tilation, destruction of diseased parts, and all defective specimens, 
leaves, and other refuse. Affected buds should also be picked 
off and burned. Susceptible varieties should not be grown where 
the disease prevails. 



VI. A riNK ROT FOLLOWINC; APPLE SCAB 
CcphalotlicciiDJi roscnin Cda. 

Craig, John, and Van Hook, J. M. Pink Rot. An Attendant of Apple Scab. 

Cornell Univ. Agl. Exp. Sta. Built. 207: 199-210. fii^s. J6-40. 1907. 
Eustace, H.J. A Destructive Apple Rot Following Scab. N. Y. Agl. Exp. 

Sta. Built. 227 : 367-389. pis. i-S. 1902. 




Fu;. 130. Pink Mold following Apple Scab. (Photograph by John Craig) 

During several seasons, particularly the autumn of 1902, apple 
scab was very prevalent in western New York, favored by a moist, 
muggy season. The scab was followed in the autumn by the devel- 
opment of a mold upon the scab spots (Fig. 130), which was at 
first white, becoming pink with a production of abundant spores. 
The fungus was identified as above, and proved to be common in 
many orchards of the state. It is a widely distributed saprophyte, 
which can be expected perhaps to cause widespread injury only 
when conditions are unusally favorable for its development. The 
greatest damage is done after harvesting, and the Rhode Island 
Greening has proved to be the variety most susceptible to its attack. 



296 



FUNGOUS DISEASES OF PLANTS 



^ 



Inoculation experiments have also indicated that this fungus may 
produce a rot through wound infections on apple, pear, quince, and 
grape. It is believed that the fungus will become injurious only 
under the conditions mentioned, and, therefore, it is necessary to 
take indirect precautions only. Prevention of the scab, in particular, 
will mean prevention of this rot, which is secondary to it. 



VII. RAMULARIA 



While the genus Ramularia is entirely parasitic, few plant dis- 
eases of serious consequence are produced. Reference has already 




"k;. 131. CiirirAr.oTHiicwM 

KOShUM 



Fig. 132. Are(ji,atk Mildew of 
Cotton 



been made to Kauiularia Tulasuci (see MycospJnerclla Fragaria, 
])age 261). 

Ramularia areola Atk. This fungus, producing what may be 
known as the frosty blight or " areolate mildew " of cotton, is very 
characteristic. Small areas of the leaf between the finer veinlets 
are occupied by the fruiting hyphae. The latter are fascicled, and 
numerous spores are borne. As a result of the abundance of the 
fruiting hyphae and the avoidance of the veins an areolate appear- 
ance is presented (Fig. 132). 



i 



FUN(iI IMPERFECTI 297 

Ramularia rufomaculans I'k. This Ranuilaria produces on the 
leaves of buckwheat {Fagopyrnm csailcntnm) blotch-hke areas cov- 
ered with abundant conidiophores. In appearance it is therefore 
very much Hke the form on cotton. 

AM 1 1. CERCOSPORELLA 

Cercosporella Persicae Sacc. The frost)- mildew of the peach in 
the United States is far more common from Maryland southward. 
It forms on the under surfaces of the leaves conidiophores and 
conidia in such quantity as to give the appearance of a surface 
mildew. It is most prevalent and often a serious disease in moist 
regions, but may be readily controlled by early spraying. 

IX. RICE BLAST 

Piricularia grisea (Cke.) Sacc. 

Fulton, H. R. Rice Blast. La. Agl. Exp. Sta. Built. 105: 1-12. Jigs. 1-12. 

I90<S. 
Farneti, R. Rivista Patalog. Veg. 2: i-ii, 17-42. 
Metcalf, Haven. Preliminary Report on the Blast of Rice. S. C. Agl. 

Exp. Sta. Built. 121 : 1-43. 1906. 

Habitat relations. The blast of rice {Oryza sativa) is reported 
from the most important rice-growing regions, and would appear 
to be a common disease wherever rice is cultivated. It causes no 
small annual loss, and the outbreaks are frequently severe. Up to 
the present time there is very little unanimity in the opinions ex- 
pressed with respect to the factors conditioning epidemics. After 
an analysis of diverse conditions reported as operative, Fulton 
believes that the factors are far more complex than generally 
stated. In South Carolina it seemed that unfavorable soil con- 
ditions are important, and in Italy lack of root aeration is sug- 
gested as the cause of " brusone," a disease with which the 
Piricularia is at least associated. 

Under favorable conditions there is a marked difference in the 
susceptibility of diverse rice varieties. At the present time it would 
seem that there are no varieties wholly free from the disease. 

Symptoms. The fungus attacks leaves and stems. Upon young 
plants the older leaves are first affected and later the younger por- 
tions of the plant. The young leaves become rapidly pale in the 



298 FUNGOUS DISEASES OF PLANTS 

affected areas and then water-soaked, dark and dead. Conspicuous 
lesions occur at the sheath nodes and upon the stems. When the 
disease appears at or above the topmost stem node, it is generally 
most serious. The maturing heads droop or fall to the ground. 
Leaves affected at the tip of the sheath also hang downward. Old 
leaves may develop spots with ash-colored centers and bright 
brown borders. 

The fungus. Conidiophores and conidia of the fungus may be 
found abundantly upon the affected parts in moist weather. The 
former emerge from the stomata, generally in clusters of two or 
three. They are ordinarily simple, fuliginous in color, septate, 
and they bear in succession several conidia, each from a tip 
which is for the time terminal. The spores are ovate, two-septate, 
and measure 24-29 X 10-12 /m. Careful inoculation experiments 
have shown that the fungus is able to induce the disease in unin- 
jured, growing plants of various ages. The fungus on rice was 
described as Piricularia Oryz(E Briosi & Cavara, but the evidence 
available indicates that the fungus concerned is identical with 
PiriciilaiHa grisca, as above given. The latter is the name applied 
to the fungus occurring in many regions upon the crab grass 
{Paniaun sangtiinalc L.). 

Control. It is unquestionably important in rice culture to pro- 
vide the most favorable conditions for a vigorous growth of the 
rice plant, and at present other direct preventive measures seem 
impracticable. It would seem that varietal resistance will in time 
offer the safest means of control. 

X. POLYTHRINCIUM 

Polythrincium Trifolii Kze. Sooty spot of clover. This fungus 
is very generally distributed upon certain species of clover, notably 
red clover {Trifoliu7Ji pratcjisc), in many parts of the world. The 
wavy or spiral character of the conidiophores and the sooty or 
fuliginous color of conidia and conidiophores are characteristic. 
This species is the only one which has been described in the genus. 
On account of the characteristics and habits of the mycelium and 
of the stroma sometimes produced, it has been assumed that the 
perfect stage would be a species of Phyllachora, and the plant 
actually bears also the name Phyllachora Trifolii (Pers.) Fckl. 



FUNGI IMPERFECTI 299 

XI. PEACH AND APRICOT SCAB 

CladosporiiDti carpopJiiliDii Thiim. 

Arthur, J. C. Spotting of Peaches. Ind. Agl. Exp. Sta. Built. 19: 1-8. 

figs. 1-3. 1889. 
Chester, F. D. Peach Scab. Del. Agl. Exp. Sta. Rept. 8: 60-63. 1896. 




Fig. I 



Peach Scau on White-fleshed Fruit 



This fungus is responsible for the well-known peach scab, a 
disease common throughout the country on peaches, and also on 
apricots. It forms, as a rule, numerous 
small, circular, sooty spots, sometimes 
confined to one portion of the fruit and 
at other times scattered over the whole 
surface. It is so common upon the 
poorer grade of market fruit that dur- 
ing an ordinary season practically none 
of the second or third quality fruit, es- 
pecially that with white pulp, is free 
from it. The spots may become scabby 
in form, and coalesced into large irreg- 
ular areas, and as a result of the injury 
severe cracking of the fruit may occur 
(Fig. 133). Twigs and leaves may also 
become affected. On the latter distinct 
spots are produced, often accompanied 
by the falling out of the affected areas, 

as with many other fungi, thus leaving ^ 

, , 1 rr /^ 1 • 1 Fig. 134. Cladospqrwm 

a shot-hole enect. (Jn the twigs the carpophilum 




lOO 



FUNGOUS DISEASES OF PLANTS 



fungus may be perennial in brown or purplish-brown spots, and 
from such areas the conidial stage of the fungus is produced the 
following spring. The fungus, shown in Fig. 1 34, is known only by 
the conidial stage, and the latter is developed throughout the season. 
In artificial culture this Cladosporium grows readily, producing a 
dense olive-black mycelium, with somewhat abnormal conidiophores 
and conidia, but no other stage has been reported in such cultures. 



XII. CLADOSPORIUM: OTHER SPECIES 

Cladosporium Cucumerinum Ell. and Arth. This fungus, like 
many other species of the genus, is occasionally parasitic. It occurs 

upon melons, producing 
sunken spots on the fruit, 
and sometimes on the 
stems. This trouble is ap- 
parent, as a rule, only dur- 
ing very moist weather, 
and under such circum- 
stances the conidial stage 
of the fungus is developed 
abundantly over the af- 
fected areas, which ap- 
pear olivaceous in color 

(Fig- 135). 

Cladosporium fulvum 
Cke. Leaf mold of tomato. 

This fungus is common 
during moist weather, pro- 
ducing on tomatoes a leaf 
blight which shows itself 
in its effects upon the up- 
per surface by a moderate 
yellow discoloration, which may eventually appear as true spots. 
On the under surface the olivaceous growth of the fungus may 
be seen. As the disease progresses the entire leaf may become 
yellowed, and often whole plants may be defoliated. The fungus 
is an active parasite, although belonging to a genus most of the 
members of which are saprophytic in habit. 




Fig. 135. Cladosporium Cucumerinum on 
Melon 



FUNGI IMPERFECTI 301 

XIII. EARLY BLIGHT OF THE POTATO 
Macrosporiinn Solani E. &: M. 

Chester, F. D. A Leaf Blight of the Potato. Del. Agl. Exp. Sta. Kept. 4 : 

58-60. 1 89 1. 
Galloway, B. T. The Macrosporium Potato Disease. Agl. Sci. 7: 370-382. 

1893. 
Jones, L. R. Potato Blights. Vermont Agl. Exp. Sta. Rept. 9: 66-88. 1895. 
Jones, L. R. Certain Potato Diseases and their Remedies. Vermont Agl. 

Exp. Sta. Built. 72 : 1-32. 1899. 
Jones, L. R., and Gkout, A. J. Notes on Two Species of Alternaria. Built. 

Torrey Bot. Club 24: 254-258. 1897. 
Stewart, F. C, Eustace, H. J., and Sirrine, F. A. Potato Spraying Ex- 
periments in 1906. N. Y. (Geneva) Agl. Exp. Sta. Built. 279: 155-229. 

1906. 
Sturgis, VV. C. Notes on " Early Blight " of Potatoes. Conn. Agl. Exp. Sta. 

Rept. 18 : 127-135. 1894. 

Habitat relations. The fungus causing the early Wight of 
potatoes was described in 1882. In 1891 it was recorded as of 
economic importance in the United States, but subject to control. 
Since that time this fungous disease has grown constantly in im- 
portance, although to a very large extent preventable. The early 
blight is common practically throughout the United States, and 
it occurs also in Canada, Europe, Asia, and Australia. 

In temperate regions the leaf blight may be found from July to 
the end of the growing season, increasing generally as the season 
advances. It may be checked, however, by periods of unusual 
drought, but it does not appear to be easily affected by lesser 
changes in conditions. 

This disease is a typical leaf blight and may be distinguished 
from the late blight already described and from such nonparasitic 
pathological conditions as tip burns and sunscald by recognizable 
leaf characters. The spots are brown, circular, or elliptical, and 
they are distinctly marked with concentric or target-board mark- 
ings. They are irregularly distributed over the leaf surface, al- 
though frequently occurring upon the borders of other injuries 
(Fig. 136). Through carefully conducted experiments (Jones) it 
has been satisfactorily determined that the fungus may establish 
itself by truly parasitic means, being capable of infecting healthy 
leaves, provided only that sufficient moisture is present to insure 
germination and vigorous growth. Nevertheless, the fungus is 



302 



FUNGOUS DISEASES OF PLANTS 



encouraged by certain weakening influences, such as the age of 
the leaf, the presence of flea-beetle injuries, etc. When large 
spots near the margins of the leaves become confluent, such ex- 
tensive areas are affected that there may result a rolling up of the 
edge, which might be mistaken for the tip burn, a disease gener- 
ally due to climatic conditions. 

The injury from the early blight results, therefore, in an early 
death of the leaves, as a result of which the vines dry up and the 
losses to the growing crop are often very considerable, amounting 

to as much as 50 per cent, l^he 
disease is said to be more likely 
to begin at the time of flowering 
and while the work of the plant is 
directed toward the development of 
tubers. This fungus produces no 
rot directly. 

This Macrosporium is found not 
only upon the potato but also upon 
tomatoes and upon the jimson weed, 
{Datura Stramoniuvi). There is 
also a very considerable difference 
in the susceptibility of the different 
varieties of potato, but at present no 
wholly resistant sorts are known, 
although the general question of 
the resistance of potatoes to diseases 
is receiving special attention in the chief potato-growing regions 
of the world. 

The fungus. Within the tissues the mycelium is light brown to 
olivaceous, and the conidiophores arise through stomates or push up 
between the collapsed epidermal cells as erect or assurgent fruiting 
hyphae 50-90 x 8-9/*. They are septate, slightly curved, and, as 
is characteristic of this genus, the conidia are produced singly, so 
far as observed, upon the host. The conidia have been described 
as " obclavate, brown, 145-370 x 16-18 /w, terminating in a very 
long, hyaline, septate beak (apical cells) equalling fully one-half the 
length of the spore (often exceeding this) ; body of spore with 5 to 
10 transverse septa, longitudinal septa few or lacking " (Fig. 137). 




Fig. 136. Early Blight of the 
Potato 



FUNGI IMPERFECTI 



303 



The germ tubes arise from any cell of the spore, and it is 
stated that they may enter the host either by means of the 
stomates or by directly penetrating the cuticle. This fungus 
grows vigorously in pure cultures. Upon prune agar it has 
been found (Jones) that the spores might be produced as a 
chain of two, and on account of this character the plant has 
been placed in the related genus Alternaria. As is, of course, 
well known, the step 
from Macrosporium 
to Alternaria is at 
best a very slight 
one, yet it should 
be remembered that 
these genera based 
upon recognizedly 
variable characters 
serve at most for 
convenience. The 
catenulate method 
of spore production 
has been reported 
only in artificial cul- 
tures in this case, 
and it is possible, 
furthermore, to ob- 
tain for various 
fungi in such cul- 
tures in general 
many variations 
from what would be considered the normal type of spore production 
upon the host. Attention may be called to the fact that cultures 
of many Stilbeas yield upon agar only simple conidiophores. Cul- 
tures of Fusarium and Gloeosporium are also modified in an equiva- 
lent manner, the stromatic development being usually suppressed. 
Species of Cercospora also produce spores in an abnormal manner. 
Upon the leaf Macrosporium may be accompanied by one or more 
species of true Alternaria, but the latter are saprophytic, as deter- 
mined by experimental work. 




Fig. 137. iM.icRospoR/uM Solani : germinating 

SroREs WITH Hyph^ entering Stomata 

(After Jones) 



304 FUNGOUS DISEASES OF PLANTS 

Control. Wherever careful spraying experiments have been made 
it has been found possible in ordinary seasons to reduce the injuries 
from the early blight to a very small minimum by the same method 
which has been recommended in case of the late blight and rot. 

XIV. ONION MOLD 

Macrosporium Sarcinida Berk. 

MiYABE, K. On the Life-History of Macrosporium parasiticum Thiim. Ann. 
Bot. 3 : 1-26. pi. I. iSSg. 

This fungus has long been associated with the onion mildew, 
and by some pathologists it is supposed that it is commonly pres- 
ent on diseased onions as a fungus of secondary importance. In 
many cases it unquestionably follows the Peronospora of this host, 
but in other cases it seems to be the direct cause of spots which 
may involve the seed stalks, or which may occur upon the older 
leaves and sheaths. It occurs in Europe, in the Bermudas, in the 
northeastern United States, and possibly throughout a wider range. 
It is conceivable that the fungus follows injuries of one sort or 
another, such as those of thrips or other insects, as well as the 
effects of the Peronospora, but it does not appear to be restricted to 
plants infested by the last-mentioned fungus. In the case of onions 
grown for seed it is especially injurious, since the seed stalks af- 
fected seldom mature their product. Miyabe established the genetic 
connection between the Macrosporium of onion and Plcospora hcr- 
bariivi (Pers.) Rab., incidentally indicating, also, that the Macrospo- 
rium agrees with the saprophytic form described by Berkeley. 

XV. MACROSPORIUM: OTHER SPECIES 

Occurring upon other solanaceous hosts are such species as 
Macrosporiuvi toviato Cke. and Macrosporium Datura Fautr. 
Several species have been reported upon onions besides Macro- 
sporhini Sarci)iula Berk, above discussed. Other species of 
Macrosporium besides the latter have also been connected with 
species of Pleospora. 

Macrosporium nigricantiiim Atkinson, Macrosporium Tabaci- 
num Ell. & Ev., and Macrosporium Iridis C. & E. are commonly 
reported as leaf spot or blight fungi of their respective hosts, cot- 
ton (Gossypium), Iris, and tobacco {Nicotiana Tabacum). 



FUNGI IMPERFECTI 



305 



XVI. BLIOHT OF GINSENG 1 

AHcniaria Panax Whetzel 

Occurrence and symptoms. The so-called "blight" is the most 
common and destructive disease of cultivated ginseng. It occurs 




Fig. 138. Blight of Ginseng: a Frequent Form of the Disease 
(Photograph by H. H. Whetzel) 



apparently throughout the eastern United States wherever ginseng 
is grown, but has not been with certainty reported west of the 
Mississippi. The disease is caused by Alternaria Panax Whetzel, 

^ This account of the blight of ginseng was kindly prepared by Professor H. 
H. Whetzel, Cornell University. 



3o6 FUNGOUS DISEASES OF PLANTS 

which, in its general characters, as regards spores (size, shape, etc.), 
is very much Hke the Altcrnaria Solaiii producing the early blight 
of potatoes. The fungus is a genuine parasite, attacking plants 
both young and old, and apparently under all conditions, although 
the disease becomes epidemic only in hot rainy weather. 

The parasite attacks all of the parts of the plant above ground, 
but never affects the roots. During epidemic periods the disease 
works with great rapidity, so that the tops of plants in an entire 
garden may be entirely destroyed within a few days. The disease 
first makes its appearance as dead brown streaks or cankers on 
the stems of the plants near the ground. This is the primary in- 
fection in the spring, and it is probably brought about through 
spores that have wintered over on the mulch or debris on the 
soil, the stems becoming infected as they come through the 
ground. This first stage is usually overlooked by the grower 
unless it becomes severe enough to cause the breaking over 
of the stems, which sometimes happens. Ordinarily the first 
observed appearance of the disease is on the leaves, which show 
rather large, more or less circular, watery spots. The tissue is 
killed outright in those spots and later becomes dry and papery 
with a brown or yellowish center. Under favorable weather con- 
ditions these spots spread and coalesce, readily killing the leaves 
and the entire top of the plant (Figs. 138, 139), so that a badly 
blighted plantation looks as if it had been drenched with scalding 
water. If the berries set before the blight has become destructive, 
they may be attacked and blasted, turning brown and dropping off 
before they can ripen. 

The fungus. The conidia or spores of the parasite are pro- 
duced in great abundance on all parts of the affected plants, but 
particularly so on the stems and blasted berries. No perfect or 
winter stage has been discovered for the fungus, but the fact that 
the spores will germinate after remaining in the laboratory dry for 
three months indicates that the conidia of the fungus are prob- 
ably carried over winter on the mulch or debris on the beds. It 
grows very readily as a saprophyte, and may pass the winter 
growing on the dead stems and mulch on the bed. The fungus 
makes its first appearance on the stems early in the spring, shortly 
after they are up, but the disease does not become destructive 



1 



FUNGI IMPERFECTI 



307 



usually before the middle or latter part of the summer ; so that the 
tops are not often killed before the middle of July or the first of 
August in New York. The parasite does not pass down into the 
root nor does it induce rot of any kind in the roots. The general 
effect on the root of the plant is to reduce its growth, and proba- 
bly where the blight continues year after year the root will be so 
weakened that it will become subject to soil rots of various kinds. 




Fig. 139. Blight of Ginseng: a Severe Attack beginning when the 
Leaves were Young. (Photograph by H. H. Whetzel) 



Control. It has been clearly demonstrated that this disease may 
be controlled by thorough spraying with Bordeaux mixture. The 
application should begin early in the spring, as soon as the plants 
come through the ground, and should be kept up throughout the 
season every ten days or two weeks. It is particularly necessary 
to spray the young plants frequently when they are coming through 
the soil in order to protect them from the primary infection. It 
has been shown that ginseng is able to stand a very strong solution 



3o8 



FUNGOUS DISEASES OF PLANTS 



of Bordeaux mixture, so that the ordinary strength may be used 
without causing any trouble. In the case of the early sprayings 
in the spring when there is apt to be cold weather, it has been 
found that plants will sometimes be injured by the Bordeaux. If 
care is taken not to apply the mixture just before a hard freeze, 
little trouble will result. 

Alternaria Violae Gall. & Dorsett^ produces a leaf spot of violets 
in the greenhouse, particularly when the houses are not well regu- 
lated with respect to dryness or moisture of the air, heat and cold, 







^jji 


|y 




m... 








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Ev 


^mi 


mBKnaESMs^^^mfKiSvSv^^^itl^Sri 




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^^^^ 




^^^P 


WS^B^Sr-^E^^^^^J^^ 






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s 



Fig. 140. Leaf Spot of Beets; a Field of Sugar Beets badly Diseased 



or when the stock is not in condition for vigorous growth. The 
old spots, as in the case of most violet leaf diseases, are white, 
although at the outset the spot is dark, and on the stem (which is 
sometimes affected) the darkened areas are often persistent. 

Alternaria Brassicae (Berk.) Sacc. This species is not uncom- 
mon upon cabbage and horse radish in Europe and America. It 
produces brown spots with concentric markings. 

1 Dorsett, P. II. Spot Disease of the Violet. Div. Veg. Phys. and Path., U. S. 
Dept. Agl. Built. 23: 1-16. //j. 7-7. 1900. 



FUNGI imperfp:cti 



309 



XVII. LEAF SPOT OF BEETS 
Cenvspora J^eticola Sacc. 

DUGGAR, B. M. Leaf Spot of the Beet. Cornell Agl. Exp. Sta. Built. 163 : 

352-359. Jigs. 56-61. 1898. 
Pammel, L. H. Spot Disease of Beets. Iowa Agl. Exp. Sta. Built. 15: 238- 

243. 1 89 1. 

Habitat relations. The beet leaf spot i.s widely distributed. Both 
in Europe and America it is a fungus of common occurrence, and 
it is believed to be more or 
less prevalent wherever 
beets are grown even to a 
limited extent. The red 
garden beet is seldom 
wholly free from this 
fungus, although many 
varieties are apparently so 
resistant that the disease 
is not an important one 
in garden or truck work. 
Much damage may be 
done to sugar beets in 
any region where summer 
rains or heavy dews are 
prevalent. Spanish and 
Swiss chard are seldom 
affected to an injurious 
extent. 

The leaf spots are at 
first very small brown 
flecks with reddish-purple 
borders. As soon as the 
spots attain a diameter of 1 inch or more they become ashen gray 
at the center, the border remaining as before so long as the blade 
is green. The spots are distributed over the leaf surface (Fig. 141), 
and they may become so numerous as to cover a large portion of 
the surface, ^et with no general discoloration of the blade. In 
time, however, the leaves blacken and dry up gradually from tip 
to base. As the leaves become parched and dry they stand more 




Fig. 141. Leaf Spot of Beets 



lO 



FUNGOUS DISEASES OF PLANTS 




Fig. 142. Effects of the Leaf-Stcjt 
Fungus: Prolonged Crown 



nearly upright, although some- 
what curled or rolled, present- 
ing a characteristic appearance 
in the field. 

Since the outer leaves are 
the first to succumb, the plant 
continues to develop new leaves 
from the bud, and the crown 
may thus become considerably 
elongated (Fig. 142), at a seri- 
ous sacrifice to root develop- 
ment, and probably at great loss 
to the sugar content. 

It has been stated by German 
observers that the leaf-spot fun- 
gus may also be found upon the 
bracts, peduncles, and even upon 
the seed pods. It is therefore 

thought that the fungus may be spread with the seed. 
The fungus. When the leaf spots 

appear gray at the centers one may 

be sure of finding the conidiophores 

and conidia of the fungus in abun- 
dance. The former arise in small 

clusters, apparently through the 

stomates at first. The base of the 

cluster is usually a few-celled stroma. 

The conidiophores are flavous, and 

ordinarily 35-55x4-5/^. The co- 
nidia are produced at the apices, and 

then by further growth of the conid- 
iophores, slightly towards one side, 

noticeable geniculations are left, and 

the conidiophores are therefore flex- 

uous. The conidia are obclavate to 

needle-shaped, hyaline, many-celled, 

75-200 X 3-5-4-5 H- (Fig. 143)- If 

produced under very moist conditions, 




Fig. 143. Cercospor.-i Beticola: 
Conidiophores and Conidia 



FUNGI IMPERFECTI 



I I 



as in a moist chamber, the length mentioned may be considerably 
exceeded. After the death of a leaf, spores may be produced over 
the entire surface. Spores found upon old leaves in the field five 
months after the beets were harvested were able to germinate. 

The fresh spores germinate readily in ordinary nutrient media, 
and pure cultures may be obtained by the poured plate method. 
After a growth of a few days the colonies show up well. The sub- 
merged mycelium develops in agar as a dense olivaceous colony, 
the new growth lighter in appearance, forming an outer border. 
The aerial growth of the colonies is finally grayish green. On 
bean pods a copious development of mycelium occurs, but such 
cultures maintained 
for two years gave 
no production of 
conidia. Abnormal 
conidia may, how- 
ever, be developed 
on this medium 
from other species 
of Cercospora in cul- 
ture. Aerial hyphae 
show a tendency to 
adhere together in 
slight strands or 




Fig. 144. Mycelium of Cercospora in Culture: 
Aerial and Submerged Forms 



clusters, and the 
small branches sug- 
gest an attempt at spore production (Fig. 144, aerial). The im- 
mersed mycelium is very irregular, with many swollen cells and 
peculiar branches (Fig. 144). I have grown about twenty spe- 
cies of Cercospora in pure cultures, but in no case has any evi- 
dence or clue been obtained as to the possible connection with 
a perithecial form. 

Control. Such experiments as have been made indicate that 
this disease can be controlled, where necessary, by Bordeaux 
mixture. Since the conidia may retain their vitality until late 
winter, it is probable that many are able to germinate after the 
seed are sown in the late spring ; early spraying is therefore 
important. 



,12 



FUNGOUS DISEASES OF PLANTS 



XVIII. EARLY BLIGHT OF CELERY 
Cercospora Apii Fr. 

Atkinson, Geo. F. Note on the Cercospora of Celery Blight. Cornell Agl. 

Exp. Sta. Built. 48: 314-316. Jig. 3. 1892. 
DUGGAR, B. M. Early Blight of Celery. Cornell Agl. Exp. Sta. Built. 132 : 

201-206. figs. 48-^0. 1897. 
Sturgis, W. C. On the Prevention of Leaf-Blight and Leaf-Spot of Celery. 

Conn. Agl. Exp. Sta. Rept. 21: 167-171. 1897. 
U. S. Dept. Agl. Rept. (1886): i 17-120. 

Habitat relations. Cercospora Apii is the cause of the chief 
disease of celery, beginning early in the season. It is common in 

the Atlantic states and well known in 
the Mississippi Valley. It is also a 
serious pest in Europe. In the early 
stages of the disease there is a well- 
defined spot with slightly raised bor- 
der ; but when the spots become 
numerous on a leaf, the latter begins 
to turn yellow, and subsequently the 
fungus develops abundantly its conid- 
iophores in indefinite areas, thus giv- 
ing the characteristic ashen or velvety 
spots of indiscriminate form. When 
a leaf becomes seriously injured it 
wilts and dries. The conidia are then 
produced in quantity over the whole 
surface, particularly during muggy 
days ; thus the dead leaves increase 
many times the chances of further in- 
fection. This disease does not usually 
appear late in the season, being fre- 
quently followed by the late blight 
(Scptoria Petroselini var. Apii) with which it has no genetic con- 
nection. This fungus also occurs on cultivated and wild parsnip 
{Pastinaca sativd) and other related plants. 

The fungus. The conidiophores and conidia of this Cercospora 
are in no way particularly characteristic. The conidiophores and 
spores are variable in size, depending upon the conditions under 




Fig. 145. Cercospora Apir : Ab- 
normal Fruiting in Culture 



FUNGI IMPERFECTI 313 

which produced ; the former measure in extreme cases 50-150 x 
4-5 iJL, and the spores, 50-280 x 4-5/"-. They attain the maximum 
size with both high humidity and temperature. The spores retain 
their vitahty for many months at least. Pure cultures of this fun- 
gus may be readily secured by the poured plate method, and the 
mycelium grows well upon bean stems and other media. In such 
cultures the conidiophores are most peculiar. They may attain a 
length of a millimeter (Fig. 145). Conidia may be produced and 
abscised for a time, leaving the customary geniculation ; then 
when the hyphae are longer, conidia-like branches arise, which re- 
main attached, and eventually serve as tme branches of perma- 
nent hyphae. The mycelium, like that of the other Cercosporae, is 
olivaceous ; but the colonies show minor peculiarities distinguish- 
ing them from other species which have been thus cultivated. 

Control. This fungus may be controlled by early spraying with 
Bordeaux mixture, 5-5-50 formula, or by repeated applications of 
ammoniacal copper carbonate. It is also claimed that partial shade, 
usually affording more equable temperature and moisture relations 
for the host, enable the plant to resist the fungus to a very large 
degree. 

XIX. LEAF BLIGHT OF COTTON 

Ceirospora Gossypina Cke. 

Atkinson, Geo. F. Sphaerella Gossypina, n. sp. the Perfect Stage of Cerco- 
spora Gossypina Cooke. Built. Torrey Bot. Club. 18: 300-301. 1891. 

Atkinson, Geo. F. Cotton Leaf Blight. Ala. Agl. Exp. Sta. Built. 41 : 58- 
61. fig. ig. 1892. 

Scribner, F. L. Cotton Leaf Blight. U. S. Dept. Agl. Kept. (1887): 355- 
357- p!- 4- 

This fungus produces a leaf blight of cotton. It is more com- 
mon on the less vigorous or old leaves, and it is generally reported 
as prevalent when for any reason the vitality of the plant is lowered. 
The spots are at first small and red, later becoming pale and finally 
brown at the centers. They are generally 1-5 mm. in diameter, 
but sometimes confluent and extensive. Conidiophores and conidia 
are at first produced ojily in the central area of these spots, but on 
leaves the vitality of which is largely lost the fungus may appear 
over large areas. Atkinson considers this fungus a conidial stage 
of SphcBrella Gossypina Atk. 



314 



FUNGOUS DISEASES OF PLANTS 



XX. CERCOSPORA: 0THP:R SPECIES 



Parallel cultures on diverse culture media of a number of 
species on related hosts would be of special interest. As in the 

case of Phyllosticta, subse- 



joo 



OVQ 



<8. 



0(S> -c 

£) 8" 




Fig. 146. Cercospora Gossypina : an 
Isolation Culture 



quently discussed, numerous 
leaf spots are produced by 
members of this genus Cerco- 
spora. Very few cross inocula- 
tions have been made, and little 
is really known concerning the 
limitations of species. When 
the host plants are different, 
minor variations in the size, 
color, septation, etc., of spores 
and conidiophores, or in the 
macroscopic appearances of 
spots, are generally employed 
in distinguishing species. 
Among many other species the following upon important hosts 
may be mentioned. 

Cercospora Viticola Sacc. This fungus produces a spot known 
as grape leaf blight. It has not been productive of serious damage 
except during unusually moist seasons. The 
spots are first evident on the lower surface of 
the leaf, and it is also upon this surface that 
the conidiophores are developed. Upon Am- 
pclopsis qninqncfolia a Cercospora is more 
commonly found, but apparently no com- 
parative study of these different forms has 
been made. 

Cercospora circumscissa Sacc. is one of the 
shot-hole-producing leaf fungi of the genus 
Prunus. It occurs on some of the native 
American as well as cultivated species of 
plums and cherries (P"ig. 147) and on the nec- 
tarine and peach. It is, however, not so important from a patho- 
logical point of view upon most of these hosts as Cylindrospoj'ium 




Fu;. 147. Cercospora 
circumscissa: Spots on 
Almond. (After Pierce) 



FUNGI IMPERFECTI 



315 



Padi, but it is important as an almond tree disease^ in California 
and elsewhere. 

Cercospora Nicotianae \\. & E. The more commonly observed 
leaf spot or frog eye of the tobacco has been reported from many 
tobacco-growing regions, but does not appear to be a disease of 




Fig. 148. Cercospora c/rcua/sc/ss.i. (After Pierce) 
a, tuberculate stroma ; /', conidiophores and conidia 

any great importance, and doubtless many different fungi are con- 
cerned in the production of spots more or less similar which have 
been reported in nonscientific literature. 

Cercospora Violae Sacc, producing white spots on leaves of the 
violet in the spring, is common in coldframe or garden culture. 

Cercospora Diospyri Thiim. is of common occurrence in the south- 
ern states on leaves and fruit of persimmon {Diospyros virginiana). 

Cercospora sordida Sacc. is the most important disease-produc- 
ing fungus of the trumpet creeper {Tcconia radicans), in the 
United States. Pale spots are produced on the leaves, and defoli- 
ation of the host often results by midsummer. 



1892 



^ Pierce, N. B. A Disease of Almond Trees. Journ. Myc. 7 : 66-77. pis. 11-14. 



.0 



i6 



FUNGOUS DISEASES OF PLANTS 



XXI. SPONGY DRY ROT FUNGUS OF APPLE 

]^oliitclla fnicti Stevens & Hall 

Stevens, F. L., and Hall, J. G. The Volutella Rot. N. C. Agl. Exp. Sta. 
Built. 196: 41-48. 1907. 

The rot of apples produced by this fungus has been reported 
from North Carolina in particular, although the disease has also 
been found upon apples from other states. The disease usually 
begins as a small spot which gradually increases to include the 
whole fruit. A characteristic of the injury 
is found in the coal black color of the older 
portions of the spot. 

The effect upon the tissues is to produce a 
rather spongy dryness, and the whole affected 
tissue is penetrated by a much-branched, 
closely septate mycelium, most abundant, 
however, close to the cuticle ; in fact, a sub- 
cuticular, hyaline stroma is formed, which 
in places eventually becomes palisade in 
arrangement. From these stromatic forma- 
tions arise a mass of erect tuberculate hyphae 
bearing numerous spores. Setae are present, 
originating in the midst of the sporogenous 
hyphae, each seta produced from the tip of a 
single hypha. These vary from 100 to 400 \x 
in length, and may be from 5 to 8 /u. in 
diameter near the base. The conidiophores arise much higher up, 
and they are relatively short, simple, fertile hyphae, each abscising 
many oblong- fusoid to falcate-fusoidal spores (Fig. 149). 

This fungus grows readily in culture upon ordinary nutrient 
media, and the color of the mycelium varies greatly, being almost 
hyaline on some and practically black on other media. Upon the 
host the sporodochia occur in concentric circles, and these are 
commonly subcuticular at first, becoming emmpent. The conidia 
are continuous, hyaline to olivaceous, and about the length of the 
normal conidiophores. The fungus has only been found on the 
apple, to which it is probably confined. The disease is easily dis- 
tinguished from the fruit spot. 




Fig. 149. Volutella 
FRUCTL (After Stevens) 



FUNGI IMPERFECTI 317 

Volutella Dianthi Atk.^ is not uncommon on carnations in 
moist situations. It attacks particularly those parts more or less 
in contact with a damp soil. In favorable conditions the fungus 
may spread with great rapidity and so weaken the plant as to 
materially inhibit the production of flowers. It may, however, 
be more severe on the cutting bench, especially when sufficient 
ventilation or drainage is not provided. 

XXII. DRY ROT OF POTATOES 

Fiisarium oxysponim Schl. 

Smith, Erw. F., and Swingle, D. 1). The Dry Rot of Potatoes due to Fu- 
sarium Oxysporum. Bureau Plant Ind., U. S. Dept. Agl. Built. 55 : 1-64. 
pis. 1-8. 1904. 

Much confusion has prevailed concerning the organisms caus- 
ing some of the diseases of potatoes both in this country and in 
Europe. Various types of potato rot have been ascribed to a large 
number of different organisms, oftentimes upon insufficient proof, 
or sometimes merely from a single observation indicating the as- 
sociation therewith of a particular fungus. 

It is very probable that many of the diseases described under 
the name of dry rot, end rot, bundle blighting, etc., are due to the 
fungus here discussed. Smith and Swingle have, by careful cul- 
tural and inoculation experiments, demonstrated the causal con- 
nection of a Fusarium with these types of disease, and they have 
taken as the name of the species here discussed the earliest de- 
scribed species of Fusarium associated with such diseases, namely, 
the one given above, and they would regard as probably synony- 
mous with this species half a dozen or more names subsequently 
applied to fungi described as producing more or less similar types 
of disease in the potato. 

Symptoms. The effect of this fungus upon the host is prima- 
rily to produce a wilt, although previous to the wilting the affected 
plants have a tendency to lie prostrate on account of the gradual 
destruction of the root system by the fungus. The fungus ap- 
parently gains entrance through the roots, and from these parts 

1 Halsted, B. D. The Carnation Anthracnose. N. J. Agl. Exp. Sta. Rept. 14: 
385-386. 1893. 



i8 



FUNGOUS DISEASES OF PLANTS 



spreads to the stem and leaves. Entrance to the tubers is gained, 
therefore, as a rule, through the stems upon which they are 
borne. The vascular system of the host plant is discolored, al- 
though frequently the tubers are not seriously injured externally 
until after they are gathered. In storage, however, the fungus 
progresses rapidly, blackening the vascular ring. At this stage 
the disease is only made apparent in the tubers by cutting them 
crosswise ; still it may be so serious as to render them unavailable 
for table purposes. Later on there may be considerable drying of 
the tubers, or soft rots due to secondary organisms may ensue. 

The fungus. 
The mycelium 
produces micro- 
conidiaand macro- 
conidia (Fig. 150) 
abundantly in arti- 
ficial cultures, also 
some chlamydo- 
spores. On boiled 
potatoes small 
greenish sclerotia 
are developed, but 
no ascogenous 
stage has thus far 
been connected 
with this species. 
ControL This fungus lives apparently for a considerable time 
in the soil, and a rotation of crops is essential whenever it be- 
comes of serious importance. Again, the use of pure seed only 
should be allowed. If necessary, inspect by cutting a large num- 
ber of the tubers which are to be used for this purpose. All 
diseased and discarded tubers should be burned and not returned 
to the land. Seed tubers which may have come in contact with 
conidia should be treated as for potato scab. 

The sleepy disease of tomatoes which has been attributed to 
Fiisarhim Lycopersici Sacc. may also be produced by the fungus 
above described, although this point has not been demonstrated 
experimentally. 




Fig. 150. FusARiuM oxysporum: Mycelium, Conidia, 

AND ChLAMYDOSPORE 



FUNGI IMPERFECTI 



319 



XXIII. FLAX WILT 



Fiisafiiim Li/ii Bolley 

BoLLEY, H. L. Flax Wilt and Flax Sick Soil. N. D. Agl. Exp. Sta. Mullt. 
50: 27-60. 

This important flax disease, which is reported as particularly 
destructive in North Dakota, seems to be characterized by symp- 
toms similar to many other diseases caused by species of Fusa- 
rium. Affected plants may be killed in the seedling stage, or 
they may wilt and die at any time during the growing period. 

The fungus has been found to be ordinarily very abundant in 
soils in which flax has been grown several successive years, and 
it is considered to be the 
chief cause of the failure 
of flax upon land where 
flax has previously been 
grown. In fact, Bolley 
points to this fungus as 
the cause of flax-sick soil. 
It would seem to be doubt- 
ful, however, if the action 
of this fungus would ex- 
plain all the peculiar rela- 
tions of flax to the soil 
upon which it has been 
grown. The fungus pro- 
duces an abundance of conidia which are typically somewhat 
curved, 4-celled, and prompt to germinate. No perfect stage of 
this organism has been found. It is believed that the old straw, 
stubble, etc., of diseased stalks harbor the fungus, and that since 
the fungus is in nature, perhaps, more particularly a saprophyte, 
there is ordinarily abundant opportunity for it to be carried over 
from one year to the next. 

Control. Control consists of seed treatment ; yet in this con- 
nection it should be said that the seed of flax are very readily 
injured by treatment even with water, and therefore much caution 
is needed to prevent injury to the seed. It is advised to sprinkle 
the seed with a formalin solution, using formalin at the rate of 




Fig. 151. China Asters dwarfed and 
killed by fusarium 



320 



FUNGOUS DISEASES OF PLANTS 



about 2 ounces to each 5 gallons of water. The treatment should 
be given while the seed are spread out on a floor or canvas, and as 
the seed are sprinkled the grain must be handled continuously with a 
shovel or rake, so that they may be moistened, but not wet, through- 
out. Subsequently, they should be handled until dry. Preceding 
this treatment, moreover, the seed should be thoroughly cleaned in 
the fanning mill. All straw, chaff, and other refuse from the pre- 
vious crop should be taken from the land, as far as practicable. 



XXIV. FUSARIUM: OTHER SPECIES 

It is apparent that the old view, which held species of the 
genus P^usarium to be largely saprophytic, must be considerably 

modified. It is a genus 
which will well reward the 
student who may devote 
himself to it. 

Reed ^ has recently de- 
scribed a disease of the 
ginseng caused by a spe- 
cies of P^usarium. The 
cultural characters of the 
organism isolated led him 
to believe that it is at least 
the same species as that 
producing the wilt of cot- 
ton and other plants, and 
although the ascigerous 
stage was not found, he re- 
ferred it to Neocosmospora 
vasinfecta (Atk.) Erw. 
Smith. 

A destructive stem blight 
(Figs. 151, 152) of the 
China aster, CallistcpJms 
hortensis Cass., has been attributed to a Fusarium, but a complete 

1 Reed, H. S. Diseases of the Cultivated Ginseng, Missouri Agl. Exp. Sta. 
Built. 69 : 43-65. figs. 1-8. 1905. 




Fig. 152. China Aster affected by 
Fusarium 



FUNGI IMPERFECTI 



321 



study of the disease does not 
appear to have been reported. 
The carnation stem wilt/' '-^ 
or rosette, is occasionally 
important both in the 
greenhouse and garden. As 
in the case of the cotton 
wilt and other similar dis- 
eases, the fungus seems to 
gain entrance through the 
root system, and its path 
of attack is mainly the 
tracheal tissues. Steriliza- 
tion of the soil seems to 
be the only effective means 
of prevention. 




Fig. 153. FusARiuM on Carnation 

RosKTTE Effect 

(Photograph by Geo. F. Atkinson) 



XXV. ROOT ROT OF THE VINE 
Dematophirra necatrix Hartig 

Hartig, R. Rhizomorpha (Dematophora) necatrix n. sp. Unters. a. dem 
forstbot. Institut zu Miinchen. 3 : 94-141. //j". ^, 7. 1883. 

ViALA, P. Monographie du Pourridie des Vignes et des arbres fruitiers. 1 18 
pp. 7 ph. 1 892. 

ViALA, P. Pourridie. Maladies de la Vigne. 248-329. Jigs. ■/4-12J. 1893. 

There is said to exist throughout a large part of Europe and 
the United States a root disease of the grapevine due to the fun- 
gus given above. In recent years investigations in the United 
States have apparently failed to develop any special disease to 
which the characteristics usually associated with Dematophora 
would apply. Moreover, the studies in Europe, unfortunately, 
develop much conflicting evidence. It would, therefore, seem 
necessary before forming any final judgment in this matter to 
await further critical study. It is quite possible that several inde- 
pendent diseases are here confused. The fungus is generally de- 
scribed as having several types of mycelium. It is stated that 

^ Atkinson, Geo. F. Carnation Diseases. Amer. Florist 8 : 720-728. 1893. 
2 Sturgis, W. C. Preliminary Investigations on a Disease of Carnation. Conn. 
(New Haven) Agl. Exp. Sta. Kept. 21 : 175-1S1. 1897. 



32 2 FUNGOUS DISEASES OF PLANTS 

directly associated with the roots, the mycelium may be at first almost 
white and flocculent, later becoming brownish-red, A rhizomor- 
phic stage is also developed, which is clearly distinguishable from 
that of Agaric2is niellens. This may be in contact with the roots, 
often beneath the bark, but it also provides for the spread of the 
fungus through the soil. It may give rise to a filamentous my- 
celium in the soil. According to Hartig tuberculate sclerotia are 
often produced from the strand beneath the bark or from the gen- 
eral mycelium upon the dead vines. From the sclerotia as well as 
from any superficial mycelium there may arise clusters of hyphae 
(conidiophores) bearing minute, simple, hyaline conidia. Pycnidial 
and perithecial stages have been described. Hartig was convinced 
that he had clearly established the parasitism of Dematophora and 
that it might be considered a fungus of much practical signifi- 
cance, not only with respect to viticulture, but also important in 
connection with the fmit interests generally, for the fungus is 
reported as of serious consequence to fruit orchards throughout 
southern Europe. Diverse opinions prevail with respect to a per- 
fect stage of this organism. 

XXVI. ANTHRACNOSE OF BEAN 
Colletotrichum Lindemiithiaiium (Sacc. & Magn.) Scribner 

Beach, S. A. Bean Anthracnose and its Treatment. N. Y. (Geneva) Agl. 

Exp. Sta. Rept. 11 : 531-552. figs. /-/. 1892. 
Fulton, H. R. Bean Diseases. Anthracnose or Pod Spot. La. Agl. Exp. 

Sta. Built. 101: 9-13. 1908. 
Whetzel, H. H. Some Diseases of Beans. Cornell Univ. Agl. Exp. Sta. 

Built. 239 : 198-214. yf^J-. 99-//J. 1906. 
Whetzel, H. H. Bean Anthracnose. Cornell Univ. Agl. Exp. Sta. Built. 

256: 431-447. figs. 2iy-222. 1908. 

Distribution and host relations. The bean anthracnose or pod 
spot ranks with the blight in importance. It is widely distributed 
throughout the limits of bean culture, and it occurs both upon 
field and garden varieties. There are probably some differences 
in the resistance of the various varieties to the attacks of the 
fungus, but there is as yet no experimental evidence to show 
that immune varieties exist. It is probable that many of the 
so-called "rust-proof" sorts indicate merely that the seed were 
selected, through a generation or two, from fields which showed 



t 



FUNGI IMPERFECTI 



323 



no anthracnose. In general, it should not be taken to indicate that 
such seed will remain free from the disease. 

The fungus attacks pods, stems, and leaves, but the most con- 
spicuous injuries are the spots upon the pods (Fig. 154). These 
appear first as small, brownish, 
or purplish discolorations, and 
as the fungus spreads radially 
the central portion becomes 
dark and sunken. Neighbor- 
ing spots may also coalesce, so 
that irregular sunken patches 
may result. The conidia in 
quantity have a pinkish tint, 
and the ulcerated areas develop 
the spores so profusely that 
this color becomes pronounced 
under favorable conditions. 
The fungus may appear upon 
the cotyledons or young hypo- 
cotyls of the seedlings, and 
this is usually indicative of 
badly affected seed. 

The fungus. The mycelium 
penetrates the affected parts 
to a considerable extent. The 
bean seeds beneath the lesions 
on the pods are commonly 
spotted or slightly discolored, 
and a careful examination 
would show that the fungous 
hyphae are also present in 
those parts. Distribution of the 
fungus another year is insured 
through such infected seed. 

Beneath the cuticle or epidermis of the older spots a stromatic 
mass of hyaline hyphae is developed, and from this arise numer- 
ous short conidiophores bearing the irregularly elliptical conidia 
(Fig. 156). Near the margins of these spore pustules, or acervuli, 




Fig. 154. Anthracnose op^ Beans 
(Photograph by H. H. Whetzel) 



324 



FUNGOUS DISEASES OF PLANTS 




Fig. 155. COLLETOTRICHUM FROM BeAN : 

AN Isolation Culture. (Photograph by 
Geo. F. Atkinson) 



a few dark colored setae are developed.^ The conidia measure 
15-19 X 3.5-5.5 A*-. They germinate readily and usually become 

septate during the process. 
Each conidium is inclosed 
by a gelatinous envelope 
which when dry glues it 
to other spores or to any 
object upon which it falls ; 
when moist, however, the 
spores are readily sepa- 
rated and distributed. 

Control. Very diverse 
methods of controlling this 
important disease have 
been suggested. Seed se- 
lection is important, but it 
is not sufficient to select 
seed which do not appear 
to be infected, for many 
minute infections will be overlooked. It is desirable, therefore, 
to select healthy seed from healthy pods, preferably from a field 
which shows the disease slightly or not at all. Whetzel's experi- 
ments thus far seem to 
indicate that this latter 
type of selection yields 
most satisfactory results. 
Spraying with Bor- 
deaux mixture, 5-5-50 
formula, is to be advised 
when the disease ap- 
pears early and when the facilities are at hand to make a thorough 
application of the spray. Burning infected material is necessary ; 
moreover, rotation of crops is important. 

1 The setae in this case are not commonly a conspicuous part of the acervulus, 
and in a cursory examination of the fungus they may be sometimes overlooked. 
In fact, this fungus was at first placed in the genus Gloeosporium. It is possible 
that climatic conditions or the texture of the host may be important in determin- 
ing the relative number of setae. 




Fig. 156. COLLETOTRICHUM LiNDEMUTHIANUM 



FUNGI IMPERFECTI 



325 



XXVII. ANTHRACNOSE OF COTTON 
Colletotrichum Gossypii South worth 

Atkinson, G. F. Anthracnose of Cotton. Journ. Mycology 6: 173-178. 

pis. iy-i8. 1 89 1. 
Atkinson, G. F. Some Diseases of Cotton. Ala. Agl. Exp. Sta. Ikillt. 41 : 

40-49. figs. g-13. 1892. 
SouTHWORTH, E. A. Anthracnose of Cotton. Journ. Mycology 6 : 100-105. 

pl. 4. figs. 1-8. 1890. 

Habitat relations. Anthracnose of cotton exists as a malady of 
some importance upon rich land in some of the cotton-growing, 
particularly the 
Gulf, states. It 
would seem that 
the fungus is widely 
distributed, but 
serious injury is 
doubtless depend- 
ent upon local con- 
ditions. 

The lesions of 
this fungus are 
more important 
when bolls and 
seedlings are in- 
fested, but injuries 
to stems and leaves 
are not uncommon. 
Upon the bolls the 
minute reddish 
spot at first evi- 
dent about an infec- 
tion center rapidly 
increases in size, 
the injured area, 
marked by a red- 
dish border, becom- 
ing black and slightly depressed. Many spots may become conflu- 
ent, so that very irregular outlines may result. As the development 




Fig. 157. Anthracnose of Cotton. 
Atkinson) 



(After Geo. F. 



326 FUNGOUS DISEASES OF PLANTS 

of conidia proceeds, in the older areas the spots vary from gray to 
bright pink. Through such injuries the boll is usually seriously 
damaged and may never open. Moreover, through the boll injuries 
the fungus may probably penetrate the seed and thus be carried over 
and distributed the following season. Seedlings may be affected 
either upon cotyledons or stem, especially upon employing diseased 
seed, and at this stage the plantlet is readily wilted as a result. 

Upon stems of the adult plant the Colletotrichum seems to be 
largely a wound parasite, although in continued moist weather 
direct injury may be induced. Upon mature leaves it is said to 
take the form of a scald, or frost effect, and it may also accompany 
other leaf diseases. 

Characters of the fungus. From a loose stroma within the tis- 
sues conidiophores of two types break through the epidermis and 
produce conidia abundantly. Small hyaline conidiophores, usually 
less than twice the length of the conidia, are more numerous, and 
they arise in a compact mass, each abscising one conidium after 
another. The spores are (see Southworth) 4.5-7 X 1 5-20 /a, oblong, 
the diameter of the middle portion sometimes less than at the ends, 
usually pointed at the base, and vacuoles may be present. The 
other form of the conidiophores, termed setae, arise later from dark 
colored cells of the stroma. These setae, which usually appear in 
clusters of 5 to 10, are of a dark olive color, 100 to 250/x long, 
tapering and septate. They bear ovate, basally pointed spores. 
The mass of conidiophores and spores produced in this manner 
constitute the acervuli. In this form an acervulus may be from 
100 to 150/A in diameter. 

The spores germinate readily in almost any nutrient media, usu- 
ally becoming once or twice septate during germination, llie my- 
celium, which grows vigorously in culture, is hyaline, flexuous, 
and abundantly septate. Short conidiophores are promptly pro- 
duced. The conidia are borne singly, but by virtue of a slightly 
gelatinous envelope they may adhere in a crown about the tip 
of the conidiophore. Appressoria are also produced by the myce- 
lium, and these give rise to other similar structures, to an ordinary 
hypha, or to a conidiophore. Such dark cells are also developed 
from a germ tube when germination proceeds in water. The setae 
have also been produced in culture. 



FUNGI IMPERFECTI 327 

Control. Adequate methods of control have not been devel- 
oped. It is important, however, to select varieties which permit 
the access of light to the bolls. Seed selection from healthy bolls 
may prove of value. 

XXVIII. WITHER-TIP AND SPOT OF CITRUS FRUITS 

Colh'totrichuni Glxosporioides Penz. 

Rolfs, P. H. Wither-Tip and Other Diseases of Citrus Trees and Fruits. 
Bureau Plant Ind., U. S. Dept. Agl. Built. 52: 1-20. pis. 1-6. 1904. 

Host relations. In practically all parts of the world in which the 
orange and other citrus fruits are cultivated this fungus is more 
or less common. The diseases or injuries produced by it are vari- 
ously known as wither-tip, leaf spot, anthracnose, canker, and lemon 
spot, depending upon the effects upon the host. The fungus is a 
far more active parasite in humid regions, and in Florida, particu- 
larly, the disease appears to be growing in importance from year' 
to year. In 1891 it was casually noted by Underwood, and since 
that time it has rapidly come into prominence as a destructive 
agent to the citrus industries. 

On orange. The wither-tip effect is particularly characteristic of 
orange trees. It may be found upon trees of all ages, affecting and 
killing back the tips of the branches. On large trees this neces- 
sarily prevents the setting of a heavy crop of fruit. The varieties 
of the orange seem to be about equally affected. The disease is 
easily distinguished from dieback (a disease not associated with 
a specific organism) by unmistakable characters, especially by the 
ashen color of the twigs where dieback effects are brown ; by 
the line or ring separating injured from healthy tissue, which is 
absent in the other disease ; by the absence of any resinous de- 
posit ; and by the frost-like killing of twigs, where in dieback 
twisted branches and the development of twigs with brown-stained 
bark are common. 

On lemon. Upon the lemon it causes not only a wither-tip, but 
also a very definite leaf spot, and from the diseased areas of the 
leaf the fungus may extend into the twigs, thus resulting in the 
wither-tip, the more acute form of the trouble. The mature fruit 
may also be affected in the form of a fruit spot. It would appear 



328 FUNGOUS DISEASES OF PLANTS 

that penetration of the fruit is probably gained through some in- 
jury or abrasion. A dark spot is invariably produced, but ordina- 
rily no rot results. The spot on the fruit, however, may not manifest 
itself before shipment to market, and therefore the quality of a 
large shipment may be materially affected. 

On the lime. Upon the lime practically all forms of the disease 
are to be seen, and it is the host which is most seriously affected. 
It occurs a:s wither-tip, and the infection is through the terminal 
bud. It may also occur as a fruit canker, and more particularly as 
an " anthracnose " on the young growing shoots. 

The fungus. According to Rolfs, the acervuli are produced in 
many of the diseased areas, whether of leaf, twig, or fruit. The 
spores are produced on short conidiophores, among which are inter- 
spersed, especially at the margin of the acervuli, certain fuliginous 
setae, from 60 to i6o/x long, and once or twice septate. There 
are, however, smaller setae throughout ; yet on tender twigs few 
setae may appear. The conidia develop from short conidiophores 
3 to i8;u., arising from a more or less definite stroma. 

Control. It has been found that the disease may be held in 
clieck by proper spraying, especially with Bordeaux mixture. The 
time of spraying, however, depends upon the form of the disease, 
wither-tip and leaf spot being preferably pruned out and the trees 
subsequently sprayed. The fruit of the lemon will not, however, 
permit of the use of Bordeaux, and the lemon spot may, there- 
fore, be best controlled by sprinkling the fruit with ammoniacal 
solution of copper carbonate before picking. 

XXIX. ANTHRACNOSE OF CLOVER AND ALFALFA 
CoUetotnchiim Trifolii Bain 

Bain, S. M.. and Essary, S. H. Selection for Disease-Resistant Clover. 

Tenn. Agl. Exp. Sta. Built. 75 (Vol. 19, No. i): i-io. figs. /-j. 1906. 
Bain, S. M., and Essary, S. H. A New Anthracnose of Alfalfa and Red 

Clover. Journ. Mycology 12: 192, 193. 1908. 

An investigation of the causes of failure in red clover growing 
in Tennessee has resulted in the discovery of an anthracnose as the 
chief agent. This fungus attacks also alfalfa, but alsike clover is 
practically immune. The fungus has been reported also from 
West Virginia and Arkansas. 



FUN(}I IMPERFECTI 329 

The fungus produces black spots on stems and petioles, very 
rarely on the leaves. It is stated that the plants seem to suffer the 
greatest injury, first, when the seedlings encounter prolonged dry 
weather ; and again, during the ripening of the seed, — when the 
effects are more severe on the stems just above the surface of the 
ground. The conidia are hyaline, generally straight and rounded, 
II-13 X 3-4 At. The setae are continuous or i -septate, fuliginous, 
apex pale, 39-62 x 4-7 /*, often sinuous or nodulose. It is improba- 
ble that any cultural methods would be effective in preventing the 
spread of this disease. Selection of seed from apparently resistant 
plants have yielded offspring which likewise developed the disease 
to less extent. It remains, however, to be seen if this may not be 
due in part to clean seed selection. 

XXX. ANTHRACNOSE OF SNAPDRAGON 

Colh'tofrichiiin AntirrJiini Stewart 

Stewart, F. C. An Anthracnose and a Stem Rot of the Cultivated Snap- 
dragon. N. Y. Agl. Exp. Sta. 179: 105-iog. 1900. 

The above fungus is, according to Stewart, the most serious 
disease of the snapdragon {AntirrJiiiinvi majns), as cultivated in 
greenhouses in the United States. It is also destructive in the 
garden. In greenhouses the greatest injury occurs generally in the 
spring and fall, and in the open during late summer. It attacks 
both stems and leaves at practically any stage of growth. 

On the leaves circular dead spots are produced, and on the 
stems elliptical sunken areas 3-10 mm. in length. The spots on 
the stems frequently become confluent, and girdling may some- 
times result. 

Small dark stromata are produced in the centers of these spots, 
each under favorable conditions becoming an acervulus by produc- 
ing short conidiophores bearing straight or slightly curved conidia, 
16-21 X 4 ft, and also several dark, tapering setae, 50- 100 /a long. 

Cuttings should be made from healthy plants only, and over- 
head watering avoided when possible. If it is necessary to spray 
young plants, Bordeaux mixture is effective ; but a fungicide which 
does not discolor the foliage should be substituted if further treat- 
ments are required. 



330 FUNGOUS DISEASES OF PLANTS 

XXXI. COLLETOTRICHUM: OTHER SPECIES 

Among numerous other species of economic importance the 
following may be mentioned. 

CoUetotrichum Lagenarium (Pass.) Ell. & Hals. The anthrac- 
nose of cucumbers, squash, watermelons, etc., is a disease of both 
leaves and fruit. On the former brown spots are produced, causing 
early maturity of the leaf ; but the more serious form of the 
trouble is on the fruit, where water-soaked, finally sunken spots 
are developed. In these spots appear acervuli producing numerous 
conidia adhering in the form of viscid masses pink in color. A 
mold-like growth of superficial hyphae may also appear in moist 
weather. In time the whole fruit may rot, saprophytic organisms 
assisting. 

CoUetotrichum falcatum Sacc. is believed to be the chief cause 
of the red rot ^ of sugar cane {SaccJiamvi officinaruui) in the 
East Indies and in the Hawaiian Islands. 

CoUetotrichum Phomoides (Sacc.) Chester ^ is the cause of a 
disease of the tomato fruit characterized by discolored, sunken 
spots. PInder moist conditions these spread quickly, become con- 
fluent, and there is produced a general decay. At first distinct 
acervuli are produced, but with the softening of the tissues a con- 
tinuous stratum of conidiophores and setae may arise. This is re- 
garded as wholly distinct from a species on peppers, CoUetotrichum 
nigrum Ell. & Halsted, described a few years earlier. 

XXXII. GLCEOSPORIUM 

The genus Gloeosporium has been discussed in part, inas- 
much as several species of this form genus have been definitely 
connected with several genera of Ascomycetes already treated. 
Specific names have been assigned to forms of this genus on 
several hundred host plants. Many of these are fungi of great 
economic importance. They are parasites whose attacks frequently 
amount to epidemics. Nevertheless, these fungi are grown in 
artificial cultures, as a rule, with the greatest readiness. Moreover, 

1 Lewton-15rain, L. Red Rot of the Sugar Cane Stem. Exp. Sta. of the 
Hawaiian Sugar Planters Assoc. Bulk. 8 : 1-44. figs. 1-13. 1908. 

2 Chester, F. I). Diseases of the Tomato and Their Treatment. Del. Agl. Exp. 
Sta. Rep. 4: 60-62. figs. S-io. 1891. 



I 



FUNGI IMPERFECTI 



331 



such cross-inoculation experiments as have been made indicate 
that many species, at least, are not closely restricted as to hosts, 
and one form might be the cause of disease in a variety of plants. 
It has seemed to be a group which would well reward comparative 
study in artificial culture, and advantage has been taken of this 
by Stoneman,! Edgerton,i and others. With particular reference 
to species of one type, those which may represent stages of the 
pyrenomycetous genus Glomerella, Edgerton says in part : 

There are many closely related forms and species and all are variable. 
They vary under artificial cultivation and probably under natural conditions. 
Many are similar enough to be considered the same species, but evidence suffi- 
cient to warrant bringing together the related forms as one species is generally 
lacking. 

In the determination of a species too much dependence cannot be placed 
upon cultural characters alone. These characters are useful, but are not suffi- 
ciently constant to justify exclusive use. 

Thus far species of Gloeosporium seem to have been definitely 
connected with three genera of Ascomycetes, as follows : Pseudope- 
ziza, Glomerella, and Gno- 
monia, the imperfect stages 
of which were respectively 
known as Glaosporimn 
Ribis (Lib.) Mont. & 
Desm., Glawsponmn fnic- 
tigcmim Berk., and Gloeo- 
sporhim nerviseqiunn Sacc. 
The imperfect form is in- 
variably the important 
stage from the phytopatho- 
logical point of view. The 
effects upon the hosts are 
in every way comparable 
to those resulting from the 
attacks of various species 

placed in the closely related genus Colletotrichum previously de- 
scribed. In fact, some species of Gloeosporium occasionally pro- 
duce a small number of setae under special conditions. Upon the 




Fig. 158. Glceosporium on Leaves of 
Norway Maple 



1 See Bitter Rot of the Apple, p. 271. 



332 FUNGOUS DISEASES OF PLANTS 

twig cankers the gloeosporial stage of the apple bitter rot fungus 
may produce these. Moreover, in artificial cultures species of Colle- 
totrichum have also yielded ascigerous stages referable to the genus 
Glomerella.^ On the other hand there is a fairly close relationship 
between extreme forms of Colletotrichum and Volutella. 

In members of both Colletotrichum and Gloeosporium it has long 
been known that when conidia germinate in a drop of water on a 
glass slide, or under certain other conditions, structures resembling 
secondary or resting spores may be formed. Hasselbring^ has 
made a special study of these and concludes : 

The spore-like organs formed by the germ tubes of the anthracnoses are 
adhesion organs, by means of which the fungus is attached to the surface of 
its host during the early stages of infection. They are not suited for dissemi- 
nation and therefore are not to be regarded as spores. The adhesion discs are 
formed as a result of stimuli from mechanical contact acting on the germ tubes. 
When growing in nutrient media the germ tubes lose their power of reacting 
to contact stimuli by the formation of appressoria. Under natural conditions 
the appressoria are formed as soon as the germ tube emerges from the spore. 

XXXIII. ANTHRACNOSE OF GRAPE 
Gloeosporium atnpelophagum Sacc. 

ScRiBNER, F. L. Report on Fungous Diseases of the Grape Vine. Anthrac- 
nose. Division of Botany, U. S. Department of Agriculture, Built. 11 : 
34-38. pi. 6. 1886. 

VlALA, T. Les Maladies de la Vigne. Anthracnose. pp. 204-247. pis. 5-d. 
figs. 60-73. 1893. 

The anthracnose or bird's-eye disease of the grape is a striking 
disease now well distributed throughout Europe and America. It 
was not observed extensively in the United States until about 1885, 
and there are few localities in which it has become a malady so 
constant in succeeding seasons as the black rot or the downy 
mildew. It is, however, a disease which may cause great injury 
when it becomes epidemic, particularly in view of the fact that it 
is not so readily treated. 

The disease occurs upon berries, shoots, and leaves, but is far more 
common upon shoots and berries. Upon the latter the well-known 

1 Edgerton. Bot. Gaz. 46, /. c. 

2 Hasselbring, H. H. The Appressoria of the Anthracnoses. Bot. Gaz. 42 : 
135-142. figs. 1-7. 1906. 



FUNGI IMPERFECTI 



333 



bird's-eye spots, or effects, are produced. At first ashen-brown 
spots appear, and as these enlarge in a more or less regular man- 
ner the central portion becomes sunken, and between the paler 
central portion and the brown outer border a band of red or red- 
purple is apparent. The unaffected portion of the berry remains 
perfectly green, but the spot may at times embrace eventually the 
entire berry. When the shoots are affected the spots are similar 
to those on the fruit except that they elongate in the direction 
of the axis, becoming prominently sunken, pale at the center, and 




Fig. 159. Glceosporium AMPELOPHAGUM : Anthracnose ok Grape 

always less highly colored. The young leaves are also affected with 
spots with pale centers and brown-red borders. 

The acervuli of the fungus appear more commonly upon berries 
and twigs. The fungus resembles very closely, in general, other 
species of Glceosporium. A large number of minute conidiophores 
are produced, each of which may originate many conidia. The latter 
may be elliptical, ovate, oblong, or even slightly constricted at the 
middle portion. These are usually 5-6 x 2.5-3.5 /a. By some it 
has been claimed that the anthracnose of the grape is the same 
fungus as that producing the bitter rot of the apple, but this is 
probably incorrect. It is quite probable that a ripe rot of the grape 



334 



FUNGOUS DISEASES OF PLANTS 



may be induced by Glouicrclla rufomacnhms, the fungus of bitter 
rot ; but the typical anthracnose has not been produced by inocu- 
lations with the apple fungus. Moreover, the species here discussed 
seems to be more closely restricted in its conditions of growth. 
Upon artificial media it grows slowly and with less vigor than is 
commonly the case with many species of anthracnose. 

Control. Experiments concerned with the prevention of this dis- 
ease indicate that the usual spraying operations as recommended 
for the black rot are not necessarily effective for the anthracnose. 
Nevertheless, it is doubtful, under ordinary circumstances, if other 
precautions need be taken. When the fungus appears in an epi- 
demic form it will be necessary not only to spray repeatedly with 
Bordeaux, but also to prune out and burn as promptly as possible 
the diseased canes and fruit bunches. 



XXXIV. ANTHRACNOSE OF RASPBERRY AND BLACKBERRY 

Glecosporiiim ]'cnctiim Speg. 

Detmers, Freda. Anthracnose of Raspberry and Blackberry. Ohio Agl. 

Exp. Sta. Built. 4 (No. 6): 124-126. ph. 3-4. 1891. 
Paddock, W. Anthracnose of the Black Raspberry. N. Y. Agl. Exp. Sta. 

Built. 124: 261-274. 1897. 
Scribner, F. L. Anthracnose of the Raspberry and Blackberry. U. S. Dept. 

Agl. Rept. (1887): 357-367- pl-5- 

This fungus produces the well-known anthracnose of raspberries 
and blackberries {Riibiis spp.), characterized by injuries of the 
canes. Raspberries are commonly more seriously affected. Small 
purplish spots appear at first, later the center becomes gray and 
sunken, giving somewhat the bird's-eye effect. Petioles and veins 
of leaves may also be affected, and the injuries are severe. Minute 
spots sometimes appear on the blade of the leaf. The acervuli 
appear frequently in the older spots. Control measures have not 
been as effective as may be possible. The pruning out and destruc- 
tion of diseased canes 'is essential, and thorough spraying with 
Bordeaux may be practiced during the early part of the season. 
Spraying alone is not ordinarily sufficient for the proper control 
of this disease. Healthy plants only should be set, and a short 
rotation practiced. 



FUNGI IMPERFECTI 335 

XXXV. GLCEOSPORIUM: OTHER SPECIES 

In addition to the preceding, and to the various fungi already 
discussed which have gloeosporial stages, the following inducing 
diseases of some shrubs or trees may be briefly cited, 

Gloeosporium Tiliae Oudem.^ occurs throughout a large portion 
of northern Europe as an important parasite of the linden {Tilia 
Uhiiifolia). In late spring the clear, circular spots appear upon the 
leaves, generally irregularly distributed and becoming with age 
xellowish brown and separated from the healthy tissue by a darker 
brown line. The spots may also occur on the leafstalks and on 
the twigs as small, sunken areas. Severe attacks upon the leaf- 
stalks cause a premature defoliation. The acervuli appear most 
abundantly upon the upper surfaces of the spots. The conidia are 
generally ovate, elliptical or falcate, and measure 10-18 x 4-6 /a. 

Gloeosporium Juglandis (Lib.) Mont, is a cause of a serious leaf 
blight of the butternut {Juglans ciiicrca). The fungus has been 
found practically throughout the range of the butternut. The effects 
of the fungus have often been severe in the northeastern states, 
where almost complete defoliation of some trees has been noted 
as early as the latter part of July in New York, and early August 
in Massachusetts. Quite generally the fungus causes a defoliation 
which is earlier than the normal. The leaves affected are covered 
with irregular brown spots, which rapidly induce ripening, and 
defoliation results. 

Gloeosporium cingulatum Atkinson ^ is an anthracnose of the 
privet {Ligustrwn vulgarc). The fungus attacks the young twigs, 
producing at first small dark, sunken spots, but eventually girdling 
and killing the twigs. It is considered distinct from Glxosporhim 
Ligiistriiunn Sacc. 

Gloeosporium laeticolor Berk., while widely distributed, occurring 
particularly upon peaches and apricots, has apparently never been 
Reported of serious importance in the orchard. 

Gloeosporium apocryptum E. & E. on leaves and young twigs 
of the Norway maple is an important disease in the nursery. 

^ Laubert, R. Eine wichtige Gloeosporium Krankheit der Linden Zeitsch. f. 
Pflanzenkr. 14: 257-262. pi. 6. 1904. 

2 Atkinson, Geo. F. A New Anthracnose of the Privet. Cornell Agl. Exp. Sta. 
Built. 49 : 306-314. figs. 1-4. 1892. 



336 FUNGOUS DISEASES OF PLANTS 

XXXVI. MARSONIA 

Marsonia Populi (Lib.) Sacc.^ is a common leaf spot or anthrac- 
nose of many species of poplar (Populus) in Europe and America. 
It is more frequently seen upon the white poplar {Populus alba). 
It is often a destructive fungus in the nursery. It may also appear 
as a twig blight. The young leaves may be killed and the fungus 
may even extend to the main shoot and branches, or it may occur 
upon the twigs in isolated black spots. When somewhat older, 
nursery stock may show black spots at the older nodes, indicating, 
apparently, infection through the leaves. 

Marsonia ochroleuca B. & C, causing a leaf spot of chestnut, is 
a fungus which, while far less dangerous to the general growth of 
the chestnut tree than the canker, is far more widely distributed, 
and seems to occur wherever the chestnut is known. It is frequently 
injurious to a noticeable extent. Klebahn^ has demonstrated a 
connection between one species of Marsonia, Marsonia Jnglandis, 
and Gnomoiiia leptostyla. 

XXXVII. PEACH BLIGHT 

Coryneum Beijerinckii Oudem. 

Smith, R. E. California Peach Blight. Cal. Agl. Exp. Sta. Built. 191 : 73- 
100. Jigs. I -1 6. 1906. 

Habitat relations. It is somewhat difficult to determine the 
extent of injury caused by this fungus, since references to a disease 
produced by this or related fungi have not always been clearly dif- 
ferentiated from other peach diseases. In recent years, however, 
this disease has been studied in California, where it has been un- 
usually prevalent, causing great destruction during 1905- 1906. 
The organism had become gradually very abundant, and the sea- 
sons were favorable to its continued spread. In general, the effect 
of the fungus is to kill the buds on the fruiting wood, to produce 
spots on the green twigs, to retard the development of the leaves, 
and to cause dropping of the fruit. Accompanying the activity of 
this fungus is a notable gumming of the twigs from the dead spots, 
this being particularly abundant during moist conditions. It will 

1 Halsted, B. D. Poplar Blight in the Nursery. N. J. Agl. Exp. Sta. Kept. 15 : 
349-396. 1894. 

2 Klebahn, H. Centrbl. f. Bakt. u. Infekskr. 15(2 Abt.) : 336. 1905. 



FUNGI IMPERFECTI 



337 



be seen, therefore, that many symptoms of the disease as described 
in Cahfornia are more or less identical with Clasterospoi'inni car- 
pophilnni (Lev.) Aderh., as described by McAlpine ^ in Australia. 
It also occurs in Algeria.^ According to Smith, the fungus could 
not be mistaken for a simple hyphomycete, as shown by the ag- 
gregate conidiophore production (Fig. i6o). The conidial stage 
of the fungus is produced both on leaves and shoots, the pustules 
appearing at the center of the spots. They are, however, not 
readily observed, since the spots on young shoots are often sterile 
and those upon the leaves may 
fall out before the production of 
spores. Perhaps the most unfortu- 
nate phase of this disease is kill- 
ing of winter buds, which of course 
greatly destroys the vitality with 
respect to fruit production the fol- 
lowing season. It is quite probable 
that this fungus is the same as 
HclmintJwsporhnn ca rpoph iln in 
(Lev.), and this is also the view 
of McAlpine. 

ControL In controlling this dis- 
ease, it has become evident that 
winter spraying is essential. The 
disease is reported to make its 
appearance early in January in Cal- 
ifornia, and generally somewhat prior to the activity of the winter 
buds. The spraying which may be given for prevention of leaf 
curl is ordinarily too late for the best results upon this blight fungus. 
It is recommended, therefore, that an additional spraying in Cali- 
fornia be given in November or December to assist in controlling 
this blight organism. If a single spraying only can be given, it is 
perhaps best to give it in December, but later than early January 
under California conditions is ineffective. 




Fig. I 



CoRYNEUM BeIJERINCKII 

(After R. E. Smith) 



1 McAlpine, D. Fungous Diseases of the Stone Fruits in AustraHa, and Their 
Treatment. 1902. 

2 Trabut, L. Le Coryneum. Maladies des arbres a noyaux. Built, agr. de 
I'Algerie et de la Tunisie 10 : 1904. 



338 



FUNGOUS DISEASES OF PLANTS 



XXXVIII. LEAF BLIGHT OF CRANBERRY 

Pestalozzia Guepini Desm. var. J^accinii Shear 

Shear, C. L. Cranberry Diseases. Bureau Plant Ind. U. S. Dept. Agl. Built. 
110: 38-39- I9°7- 



This fungus is often found upon the cranberry, but it is 

less of minor importance as affecting the production of berr 

occurs upon fruit and leaves. The appear- / 

ance of affected berries is not particularly 

characteristic. The conidia are produced 

in quantity upon affected leaves placed in a 

moist chamber. The conidia are usually 

four-septate with the three central cells 

dark colored. The hyaline apical cell is 

furnished with from three to four filiform 

h 



doubt- 
ies. It 





Fig. 161. PiiSTAi.ozziA Guepini. (After Shear) 
a, acervulus ; h, conidia ; c and </, germinating conidia 

appendages, and the basal cell has a single shorter appendage. 
It is interesting to note that in the germination of this fungus 
one or more germ tubes are developed from the basal hyaline cell. 
The fungus grows vigorously in artificial culture. The mycelium 
is hyaline, and it develops a pinkish color when the acervuli are 
formed. The spores appear in about ten days after sowings are 
made if conditions arc favorable. 

Pestalozzia Hartigii Tub. is a fungus of importance in forest 
tree nurseries where it attacks the seedlings of young trees of pine 



FUNGI IMPERFECTI 



339 



and other conifers, as well as those of some deciduous trees, caus- 
ing a shrinking- of the bark around the young stem, and later a 
swelling above the injured area. The affected portions may be 
killed, and the injury results in time in the death of the plant. 



XXXIX. SHOT-HOLE DISEASE OF PLUM AND CHERRY 
Cylindrosporinm J\uii Karst 

Arthur, J. C. Plum-Leaf Fungus. N. Y. Agl. Exp. Sta. Rept. 8: 293- 

298. [figs. 6-10. 1889. 
Stewart, F. C, and Eustace, H. J. Shot-Hole Fungus on Cherry Fruit 

Pedicels. N. Y. Agl. Exp. Sta. Rept. 20: 146-148. 

Host relations. Many of the leaf-spot fungi occurring upon 
certain varieties of plums, cherries, and other stone fruits are to a 
considerable extent " shot- 
hole "fungi. In such cases 
the more or less circular 
injured area is separated 
by a line of cleavage from 
the healthy tissue, the in- 
jured tissue within this 
area promptly contracting, 
drying, and falling out. 
Cylindrosporium is respon- 
sible for the greater portion 
of this shot-hole trouble on 
many varieties of plums 
and cherries in America. 
On some varieties of the 
domestica type, as also on 
some cherries, the fungus 
may be common, produc- 
ing spots only, or with 
inconspicuous shot-hole 
effects. This is also true 
of the Mahaleb cherry. 
The Japanese plums, on ^^^ ^^^ Shot-Hole Disease of Choke 
the other hand, show a Cherry 




340 



FUNGOUS DISEASES OF PLANTS 



1 



very pronounced shot-hole effect. Varieties of Priimis aniericana 
are frequently free from this fungus. 

Where a species or variety is subject to shot-hole diseases a shot- 
hole effect may also be produced upon the leaves by spraying with 
any substance injurious to the leaf. When the 
leaves are so severely injured that the spots coa- 
lesce, the large irregular pieces may fall out in 
the same manner as just indicated. In any 
case the effects of shot-hole troubles on the leaf 
are frequently very severe, so that practically 
complete defoliation of the trees may take place 
by midsummer. 

The fungus. In many cases the development 

of the acervuli of the fungus is not evident before 

the diseased areas have fallen away, but varieties 

in which the injured areas are persistent exhibit 

the fruiting pustules in great quantity. In such 

cases the spores may be seen to issue from the 

acervulus in tendril-like masses which are quickly 

spread out over the surface by dew and other 

agencies, appearing at first as a pale or ashen 

coating, becoming darker after a few days. The conidiophoric 

layer is often extensive and closely beset with the minute conidio- 

phores (Fig. 164). The spores are curved and measure ordinarily 




Fig. 163. Culture 
of cvl/ndrospo- 

RIUM PaDI 





Fig. 164. Cylindrosporium Padi 
a, section of acervulus ; 3, conidia, some germinating 



FUNGI IMPERFECT! 341 

48-60 X 2 /i.. They germinate readily, and evidently require but a 
few days' incubation after infection for the production of the char- 
acteristic shot-holes upon susceptible hosts. 

No ascogenous stage of this fungus is known, and there is some 
doubt as to the ordinary method of wintering over. Stewart, how- 
ever, has found the pustules of this fungus on the twigs of cherry, 
and it is quite probable that this is one method of insuring its 
transmission from season to season. 

Control. This, as well as other shot-hole-producing fungi, may 
be controlled by the use of neutral or alkaline dilute Bordeaux mix- 
ture, although the use of Bordeaux may be accompanied by in- 
juries to the foliage. Weather conditions seem to affect greatly 
its relations to foliage injuries, and this is particularly true with 
respect to the peach and Japanese plums. In any case, however, 
thorough spraying with strong Bordeaux should be given in the 
early spring, whereas proper cultivation should be expected to de- 
stroy leaves harboring the fungi from the previous year. 



XL. FRUIT SPOT OF APPLE ^ 

Cylindrosporium Pomi Brooks 

Brooks, Charles. Fruit Spot of Apple, a Morphological and Physiological 
Study. Built. Torrey Bot. Club 35 : 423-456. p/s. sg-jj. igoS. 

Occurrence and symptoms. This disease is of common occur- 
rence in New England and is found in New York, Michigan, 
Ontario, and probably in other sections of the United States and 
Canada. The Baldwin is especially susceptible, but nearly every 
New England variety is more or less affected. 

The disease appears about the middle of August as minute spots 
or specks on the surface of the apple. At first these are indicated 
merely by a deeper red color of the skin, if situated upon the 
colored part of the fruit, or by a green color, if situated upon the 
lighter portion. As the apple ripens the spots enlarge and many 
of them become brown and sunken, giving the fruit an unsightly 

1 This account of the fruit spot was kindly prepared by Professor Charles 
Brooks, New Hampshire College, Durham, N.H. 



542 



FUNGOUS DISEASES OF PLANTS 



1 



appearance which often greatly depreciates its market value. The 
tissue beneath the spots is dry and brown. 

The fungus. The first studies upon this disease seemed to indi- 
cate that it was not produced by a fungus, but recent studies have 
demonstrated the causal relation of a fungus which seems to be 
properly a species of Cylindrosporium, as the title suggests. The 
mycelium is hyaline, septate, and intercellular. Chlamydospores 
are common in the host tissue. In late stages of the disease a 
compact stroma develops just beneath the epidermis and finally 





Fig. 165. CvL/xDRospoJi/rM Pomi. (Photographs by Charles Itrooks) 
(7, spot induced by inoculation of apple ; /', mycelium in agar 

breaks through it to expose spores and sporophores. The spores 
are hyaline, from one to five celled, and variously cur\'ed and con- 
torted. They are from 2 to 2.5 /x in diameter and from 1 5 to 80 /x long. 
The chlamydospores and stromata are probably the agencies that 
carry the fungus over the winter. Under ordinary conditions of 
preparing separation cultures this fungus does not readily grow, 
and agar will ordinarily dry out before the fungus becomes notice- 
able. On this account it has seemed to be a difificult organism to 
isolate. As a matter of fact, however, under ordinary constantly 
moist conditions or in liquid media it grows readily.^ 

Infection probably takes place in July or August when the stomata 
are being torn open and the protecting layers of the lenticels are 
not yet formed, a season when the metabolism of the apple is 
extremely great and the transpiration stream necessarily large. 

1 The " Stippen " disease, long known in FAirope and now reported from several 
parts of the United States, is regarded as entirely distinct, and probably not of 
fungous origin. 



FUNGI IMPERFECTI 343 

Control. This disease is readily controlled by spraying with 
Bordeaux, and weaker fungicides are often very effective. Spray- 
ings made as late as July have been found to entirely prevent the 
disease, 

Cylindrosporium Chrysanthemi Ell. & Dearn^ produces blotches, 
commonly termed blight, upon the leaves of some varieties of the 
cultivated chrysanthemum. It may become epidemic at the time 
that the flowers are opening, apparently due to lessened vitality of 
the lower leaves. 

XLI. HEART ROT AND BLKiHT OF 15EETS 
Phoma Beta' Frank 

Frank, B. Ueber die biologischen Verhaltnisse des die Herz und Trockenfaule 
der Riiben erzeugendcn Filzes. Ber. d. deut. bot. Ges. 13: 192-199. 
1895. 

Frank, B. Die Pilzparasitiiren Krankheiten der I'flanzen. /.(. pp. 399-403. 

Kruger, F. Die bis jetzt gemacht Beobachtungcn iiber Frank's neuen Riiben- 
pilz Phoma Betae. Zeitsch. f. Pflanzenkr. 4: 13-20. fig. i. 1894. 

Habitat relations. This is one of the most serious diseases of 
the sugar beet in portions of Germany, Austria, and France. It 
begins to manifest itself as a rule in August by blackening and 
drying of the younger heart leaves, and later older leaves also suc- 
cumb, so that before the period of harvesting all the leaves may 
be dead and merely the beet stub remain. In cases where the beets 
are grown for seed, the fungus may also be found upon the seed 
stalks and cases. It is thought that this is one means by which 
the fungus may pass over from one year to the next. From the 
affected leaves, particularly along the course of the fibrovascular 
bundles, the browning and general discoloration of the tissues ex- 
tend into the tissues of the root, and there rot sets in. If the 
disease begins early in the season great injury may be done. It is 
considered probable that this organism was a chief agent in the 
great losses sustained by beet growers in Europe during the mid- 
dle of the nineteenth century, and the organism was certainly 
again unusually prevalent and destructive in 1 892-1 893. Frank 
considers the Phyllosticta tabifica Pril. & Del. to be the same 

^ Halsted, B. D. Recent Chrysanthemum BHght. N.J. Agl. Exp. Sta. Rept. 15 : 
365-368. 1894. 



344 FUNGOUS DISEASES OF PLANTS 

organism as the one here described. It was also thought by these 
French observers that a Sphaerella which was found associated 
with the Phyllosticta might be a perfect stage of the latter species. ^ 

Pycnidia are produced over practically all the dead portions of 
the plant, especially, however, on the leaves and leafstalks. These 
are small, more or less spherical bodies, with slightly depressed 
ostiola ; pycnidia measure up to 200 /u, in diameter. The fungus 
grows readily in artificial culture media, and it has been used by 
Saida in some interesting experiments on the fixation of atmos- 
pheric nitrogen. Frank states that the spores may remain alive in 
moist soil throughout the winter without germinating, and then, 
upon being placed in beet decoction, germination will promptly 
proceed. 

Control. Spraying experiments have not yet given complete satis- 
faction. Care should be taken to destroy such remains of the previous 
crop as is practicable, and the treatment of seed with Bordeaux 
mixture is desirable where disease abounds. Fortunately this fungus 
has not made its appearance in this country up to the present time. 

XLII. DRY ROT OF SWEET POTATO 

Phoma Batatce Ell. & Hals. 

Halsted, B. D. Some Fungous Diseases of the Sweet Potato. Dry Rot. 
N. J. Agl. Exp. Sta. Built. 76: 23-25. Jig. 16. 1890. 

This fungus is not uncommon in New Jersey, but it is not 
to be considered one of the more serious enemies of the sweet 
potato. A comparative study of this species and of forms upon 
related hosts has not been made, and it is possible that it may be 
referred to a species described earlier. It attacks the root, which 
shows the effect of the invading organism only by a gradual shrivel- 
ing and discoloration of the affected areas. The whole root may 
become affected, and eventually dry and powdery. The pycnidia 
appear upon the surface in large numbers, and the fungus spreads 
rapidly during storage of the roots under moisture conditions. 
The effects of this fungus are frequently complicated by those of 
other organisms attacking the root, especially certain forms pro- 
ducing soft decay. 

^ Bull. Soc. Myc. de France 7 : 15-19. 1891. 



I 



FUNGI IMPERFECTI 



345 



XLIII. SEEDLING STEM BLIGHT OF EGGPLANT 

Phoma Sohitii Hals. 

Halsted, B. D. Some Fungous Diseases of the Egg Plant. N. J. Agl. Exp. 
Sta. Rept. 12: 277-279. 1891. 

This fungus has much the habit of a damping-off fungus, infest- 
ing the young seedlings of eggplant near the surface of the ground 
before they are removed from the hotbed. The diseased portion 




Fig. 166. Blight of Snapdragon; Plants at the Right and Left, 

INOCULATED WITH PhOMA HERBARUM {}) : CENTER PLANT, CONTROL 

is first water-soaked in appearance. Later this area shrivels, and 
the diameter is much less than that of the healthy stem beyond. 
Infected seedlings seldom survive. The pycnidia are produced 
abundantly on the drying areas. 



XLIV. PHYLLOSTICTA 



Phyllosticta Paviae Desm. The leaf blotch caused by this fungus 
is probably the most important malady of the horse-chestnut. The 
irregular spots develop rapidly as the season advances, and the 
larger part of the leaf may become involved, from the margin to 



346 



FUNGOUS DISEASES OF PLANTS 



the midrib, as if sunburned. Eventually the leaves fall prematurely 
and the vitality of the tree is greatly affected. The perithecia appear 
on the upper surface of the leaves, but are not usually present, at 
least abundant, over the whole affected area. 



i p 


■ 


^^v 


■■ 


r ' if 








^-^^^__^ 




p^^iii 


^^^^^^^ 




• 






^V^ 








^^^^ 






1 lihf.' ^4i 


^^^l^y 


M 


*^^^H 


^^. _; # ^^ 


^^^H 


1^ 


^^^^^^^^H 


^llgglg^^ 



Fig. 167. Phvi.lost/cta SOI. iTAR/.i: AvvL^ Blotch 



Phyllosticta hortorum Speg.^ occurs both upon leaves and fruit 
of the eggplant {Solamim Melongend), producing upon the latter 
soft spots which become shrunken and decayed, rendering the fruit 
worthless. 

Phyllosticta solitaria K. & E. A fungus producing a destruc- 
tive fruit blotch'^ of the apple in the South has recently been 
identified as the above species. The disease is more common 
upon the light colored varieties of this fruit. 

1 Ilalstcd, V>. I). Some Fungous Diseases of the Egg Plant. The Leaf-Spot 
Fungus. N. J. Agl. Exp. Sta. Kept. 12 : 279-281. 1890. 

'^ Scott, W. M., and Rorer, J. B. Apple Blotch. Bureau Plant Ind., U. S. Dept. 
Agl. liullt. 144: 1-28. pis. 1-6. 1909. 



FUNGI IMPERFECTI 



347 




Phyllosticta maculicola Hals.^ is the cause of a very common 
leaf spot of several species of Dracaena and Cordyline. The spots 
are characterized by pale centers and reddish or purplish borders. 
The disease is sometimes severe in greenhouses where it has long 
been allowed to proceed unchecked. It is, however, readily pre- 
vented by spraying with potassium sulfide 
solution. 

Phyllosticta Ampelopsidis Ell. & Mart, is 
perhaps closely related to the fungus causing 
black rot of the grape. It has been injurious 
during some seasons to the Boston or 
Japanese ivy {Ampclopsis V^citchii). 

Phyllosticta Catalpae Ell. & Mart.^ is 
commonly found associated with Maav- 
sporiinn Catalpcs on the leaves of several 
species of catalpa, but it is to the former 
fungus that the production of the spot is 
now ascribed. 

Phyllosticta Violae Desm. occurs upon 
the violet and the pansy, often causing 
blotch-like, pale spots which may result in 
considerable injury. 

Phyllosticta Magnoliae Sacc. produces a 
very definite spot disease on the leaves of 
Magnolia grandiflora in Europe. 

Phyllosticta Pyrina Sacc. was long sup- 
posed to be a chief cause of the apple leaf 
spot so common in the United States. 
Recent work indicates that the spot is in general primarily due to 
Sphseropsis, and that the Phyllosticta is to be regarded as taking 
a minor part in the production of the injury. In fact, the failure 
of inoculation experiments (see Sphaeropsis, p. 352) appear to 
demonstrate that the latter is saprophytic, at least with respect 
to penetration. 

1 Halsted, B. D. Blights of Dracaenas. N. J. Agl. Exp. Sta. Kept. 14: 412. 
1893. 

2 Scribner, F. L. Leaf-Spot Disease of Catalpa. U. S. Dept. Agl. Rept. 
(1887): 364-369. 




I 



Fig. i(ic. Ukai .kina 
Leaf Blight 



348 FUNGOUS DISEASES OF PLANTS 

XLV. BLACK ROT OF SWEET POTATO 
Spharonema Jinibriatum (Ell. & Hals.) Sacc. 

Halsted, B. D. Some Fungous Diseases of the Sweet Potato. The Black 
Rot. N. J. Agl. Exp. Sta. Built. 76: 7-14. figs. 3-10. 1890. 

Halsted, B. D., and Fairchild, D. G. Sweet-Potato Black Rot. Journal of 
Mycology?: i-ii. pis. 1-3. 1891. 

The black rot of the sweet potato is one of the most destructive 
diseases of this host, and it is known to occur from New Jersey 
southward practically throughout the Atlantic coast region. The 
distribution of the fungus, however, is not completely known. The 
disease may appear in the seed bed, resulting from the use of 
infested seed roots. The disease upon the seedlings is known as 
black shank, due to the black spots or discolorations on the roots 
and young stems. The commercial root may be infested either 
as a result of planting diseased slips, or the infection may be due 
to the presence of the fungus in the soil. Upon the full grown 
root the disease appears in the form of dark patches or decayed 
spots, which, upon more careful examination, and especially upon 
removal of the skin, will appear green. These spots vary in size 
from minute flecks to extensive areas involving practically the whole 
root. When the roots are diseased there is no appearance of the 
vegetative parts which suggests the presence of the parasite. 

The fungus. The mycelium consists of septate, much branched, 
thick-walled, olivaceous hyphae, which are commonly intercellular. 
The cells in the region invaded are robbed of starch, and the cell 
walls are brown and often collapse. The fungus has many fruiting 
stages which may be briefly referred to. Two kinds of conidia are 
produced, one within the tissues consisting of simple, ovate, green- 
ish cells, abscised from terminal or lateral branches. Upon the 
surface of the diseased area, or in culture, there are also produced 
minute, hyaline conidia. The latter are developed endogenously, 
more or less as described for a similar phase in the case of the 
root rot of tobacco, Thiclavia basicola. The pycnidial form is 
produced within the diseased areas, and it is also readily developed 
in artificial cultures. It consists of a flask-shaped pycnidium, with 
extremely long neck. The bulbous portion is from 96 to 224 /i in 
diameter and the neck from 395 to 608 /x. in length, and 24-34 /i 
wide at the base, tapering to 12-14 /*-. The method of spore 



FUNGI IMPERFECT! 349 

production in the pycnidium has not been clearly made out, but 
the spores are unicellular, and, when mature, ooze out from the 
tip of the flask-shaped body, adhering in masses. They are more or 
less subglobose or oblong, hyaline, and measure 5-9 /"■ in length. 
Upon immersion in water they increase greatly in size and readily 
germinate. 

When the mycelium has developed to a considerable extent in 
the root, sclerotia of large size appear. It is believed that these 
sclerotia may be properly a phase in the life history of this species, 
and that they may also be important in the perpetuation or spread 
of the fungus. This fungus will continue its growth and develop- 
ment upon the stored roots, and also upon the remnants of the 
crop left in the field, so that special care must be taken not only 
with respect to the quality of the roots used at the time of planting, 
but also to the prevalence of the disease during previous years in 
the fields where potatoes are to be grown. 

The sunken area and the greenish character of the diseased 
portion enables one readily to distinguish the effects of this fungus 
from those produced by the common black mold, Rhizopiis nigri- 
cans Ehr., which is the organism causing the typical soft rot of this 
crop. The latter disease is not discussed in this work. 

Proceeding from the mycelium within the tissues the Sphaero- 
nema has been readily cultivated upon various artificial media. In 
cultures upon sweet potato agar a profuse mycelium is developed. 
The submerged hyphas are olive brown in color and contain abun- 
dant oil droplets. All three types of spores are produced, aerial 
hyphae originating the endogenous spores, and submerged sporo- 
phores producing the olivaceous conidia. Normal pycnidia develop 
in culture in a week or more. The disease has been produced in 
healthy roots by inoculation with the hyaline conidia and with the 
pycnospores from pure cultures. 

Control. Seed roots for planting purposes should be carefully 
selected and no slips should be taken from plants in the seed beds 
showing disease. Rotation of crops is necessary to rid fields of 
this fungus. Apparently no experiments of interest have been 
made to determine the possibility of preventing the spread of the 
fungus in stored roots. Nevertheless, any conditions favoring the 
accumulation of moisture would be favorable to the organism. 



350 



FUNGOUS DISEASES OF PLANTS 



1 



XLVI. BLACK ROT AND CANKER OF POMACEOUS FRUITS 
Sphceropsis Malorum Pk. 

Halstki), B. D. The Black Rot of the Quince. N. J. Agl. Exp. Sta. Built. 

91 : 8-IO. 1892. 
Paddock, Wenijpxl. The New York Apple-tree Canker. N. Y. Agl. Exp. 

Sta. Built. 163: 331-360. ph. 28-jj. 1899. 
Paddock, Wendell. Ibid. (Second Report) N. Y. Agl. Exp. Sta. Built. 

185: 205-213. 1900. 

Habitat relations. Under the specific name given above a fruit 
decay of apples, quinces, and pears has become well known although 




I'ni. 169. Sfh.ekopsis AIalorcm on Apple. (Photograph by 
H. H. Whetzel) 

not serious in the LInited States. More recently it has developed 
that this fungus is likewise the cause of an important form of can- 
ker on trunks and limbs of the same fruit trees. It has been ex- 
tensively studied only in New York (Paddock). Owing to the 
occurrence, however, of a variety of cankers on the apple tree, this 
one is frequently designated " the New York apple canker." 
This canker has been found to occur in many of the northeastern 



FUNGI IMPERFECTI 



351 



and northern central states, as well as in Canada, and it is not 
improbable that it is more or less distributed throu<<hout the 
country. Under other scientific names, moreover, it may also be 
known botanically, at 
least, in Europe. 

As a rot of fmit the 
fungus is more generally 
known in America. It 
is a brown rot, begin- 
ning as a small spot, fre- 
quently near the bud end 
of the fruit, and spread- 
ing until the whole fruit 
may be involved. There 
is not such characteristic 
shrinkage of the tissues 
as in the case of the bit- 
ter rot. The pycnidial 
pustules may begin to 
appear when the spot is 
only half an inch in di- 
ameter, or they may not 
become evident until the 
entire fruit is decayed. 
This rot often attacks 
the fruit on the trees, 
yet it is far more com- 
mon upon the neglected 
fallen fruit (Fig, 169), 
which is a great source 
of danger to the health 
of the tree. In the mild- 
est form the canker is believed to cause merely a greater rough- 
ening of the bark, an injury which may occur as a single spot, 
or which may extend along the limb for a distance of several feet. 
In the most serious cases it first destroys the bark, well-marked 
depressed areas being developed, about which local swellings of 
the limbs occur, and in these affected areas the wood at the center 




Fig. 170. The Sph.^ropsis Canker of Apple 
(Photograph by H. H. Whetzel) 



352 FUNGOUS DISEASES OF PLANTS 

may be exposed, or extensive wounds may result. The disease is 
more common upon the larger limbs of older trees, but trunks and 
twigs are not exempt, and young trees may suffer. When complete 
girdling results, the limb is killed, yet serious consequences may 
gradually develop without girdling. Fig. 170 shows an early stage 
of this canker. 

Infection is probably most frequent in the spring. It is believed 
upon good evidence that the worst wounds occur only when the 
fungus gains entrance to the edge of the wood through wounds. 
Trees which sunscald badly on the parts exposed to the direct 
rays of the southwest sun are as a rule subsequently infested with 
canker. In New York the Spitzenburg and Twenty Ounce are 
mentioned as the most susceptible varieties of apple to the limb 
canker, while Baldwin, Wagoner, Greening, and King follow in 
the order given ; the Tallman Sweet was reported practically 
resistant. The susceptible varieties of pear are not known. In 
some cases, at least, the body blight of pear is also to be attributed 
to this canker organism. 

Infrequently a Sphaeropsis has been found upon the leaves of 
the pear, and this form appears to be similar to the canker fungus.^ 
It is thought that general neglect, crowding, lack of pruning, 
etc., encourage the canker, although it may appear in vigorous 
orchards. There would appear to be absolutely no doubt that the 
rot of apples, pears, and quinces is due to the one fungus. Trans- 
fers of this organism are readily made. Paddock made many pure 
cultures as well as many transfers of the canker strains to fruits 
and vice versa, also to a variety of other hosts. The inoculation 

1 From extensive experiments made during 1907 by Scott and Rorer, it has 
been demonstrated that the common leaf spot of the apple, as it occurs east of 
the Rocky Mountains, is also generally traceable to Sp/urropsis Maloriim Pk. as 
a primary cause. The other fungi which have been associated with the apple 
spot, such, for instance, as Phyllostida Pyri)ia Sacc. and Phyllosticta limitata Pk., 
have not been found to induce leaf spots upon inoculation. From young spots 
the Sphaeropsis colonies are constantly plated out, and the other fungi mentioned 
were only present during the later stages of the disease. Moreover, inoculation 
experiments with the former have almost invariably yielded positive results 
within from five to ten days. These observers are of the opinion, therefore, that 
neither Phyllosticta nor other forms which may be found upon those spots are of 
any special importance in the apple orchard. (Scott, W. M., and Rorer, J. B., 
Apple Leaf- Spot caused by Sphaeropsis Malorum. Bureau Plant Industry, U. S. 
Dept. Agl. Built. 121 : 47-54. 1908.) 



FUNGI IMPERFECTI 353 

experiments suggest that Sphceropsis Mali (West) Sacc. on bark, 
Sphceropsis cinerea (C. & E.) Sacc, and Sphceropis Maloiiim Pk. 
are properly the same fungus. Until, however, more careful com- 
parisons shall have been made, we may continue to refer to this 
disease-producing fungus as Sphceropsis Malonmi. It may be, 
moreover, that it occurs upon many other hosts. 

The fungus. The mycelium is sooty brown or olivaceous 
within the tissues. It penetrates the bark readily but may not 







^%\^ >; 












S-"- to 


^ 


^^ -^ ^^'^k. 




"^^^^bVa^^^H^"^ 


rv*' 


^rA *^ ^ "^^^Hk^- 3 ^ 






> 


1 *--'^^ 


ii^ 






^^PEt^ 


f 


r 






/ 








~- 






'n 


- -- 









Fig. 171. Sph.-eropsis Malorum : Mature Pycnidium. (Photograph 
of a drawing by F. C. Stewart) 

extend far into the wood. The pycnidia are erumpent, usually sur- 
rounded by a broken epidermis (Fig. i/i)' ^^^ they appear in 
cross section somewhat depressed-conical at the apex. The spores 
are oblong-elliptical, brown, and usually about twice as long as 
broad, measuring in general 22-32 x 10- 14 /a. It has been found 
that the average sizes of the spores of the forms on apple, pear, 
and quince vary according to the host and part attacked. The most 
noteworthy difference is that upon the limbs the spores are smaller 
than on the fruits. The spores seem to retain their vitality for a 
considerable period of time, having been germinated after being 
stored for a year in the laboratory. On agar the fungus develops 



;54 



FUNGOUS DISEASES OF PLANTS 




Fig. 172. Isolation Culture of 
Sph^r ops/s A/a l or um 

;'ivc a winter spraying with white- 



effuse colonies, the aerial portions of which are at first gray, be- 
com.ing darker with age. The pycnidia may sometimes be pro- 
duced in agar and also upon 
various solid media in tube 
cultures. 

Control. Preventive meas- 
ures have not been carefully 
worked out. Under ordinary 
circumstances orchards in 
good condition will suffer least. 
Advantage may also be de- 
rived from treating the limbs 
and trunk thoroughly with any 
"" cleaning up " washes, or with 
Bordeaux mixture. P^or varie- 
ties susceptible to sunscald, 
after which the canker may be 
common, it is recommended to 
wash. Pruning and scraping may also be required, and along with 
this the wholesale destruction of affected limbs or fruit. 

XLVII. RASPBERRY CANE BLIGHT 

Coiiiof/iyrii/in FiickcUi Sacc. 

Stewart, F. C. Raspberry Cane Blight and Raspberry Yellows. N. Y. (Geneva) 
Agl. Exp. Sta. Built. 226: 331-366. pis. 1-6. 1902. 

Habitat relations. This is a fungus which, as a disease-produc- 
ing organism, has been known only a few years ; and it may be 
that the species is new. The botanical name given above is applied 
to a fungus which was described as occurring on a variety of shrubs 
and trees, the genus Rubus being among the hosts mentioned. 
Stewart and Eustace have tentatively referred the fungus caus- 
ing raspberry cane blight to this variable species. 

The cane blight is a widespread disease in New York state, 
and doubtless quite common throughout the country upon rasp- 
berries. It is essentially a wilt disease (Fig. 173), and the principal 
damage results to the fruiting canes. In some instances, however, 
young canes may be killed during the first season of growth. 



I 



FUN(}I IMPKRFECTI 



;55 





%. 




3ioC 


> 


m^ 



Fig. 173. Rasi'berry Cane Blight. (Photograph by F. C. Stewart) 

Stewart states : 

The whole cane may be involved or only a portion of it. Often a single 
branch is killed while the remainder of the cane continues alive and appar- 
ently normal. In the majority of cases only a part of the cane dies. With 
black caps the disease frequently starts in the old stub left in pruning. From 



356 FUNGOUS DISEASES OF PLANTS 

this point it gradually works downward, killing first the uppermost branch, 
then the next lower one, and so on until by the close of the berry harvest one- 
half of the cane or more may be dead. On black caps the disease also shows 
a tendency to work down one side of the cane, killing the bark and discolor- 
ing the wood on that side, while on the other side the bark remains green. 

The disease occurs both upon black and red varieties of the 
raspberry, and it is thought that it may also injure dewberries. 
Cuthbert, Marlboro, Ohio, Gregg, Kansas, Superlative, I.X.L,, 
and Pride of Geneva are varieties of raspberry which have been 
found to have been much injured in New York, while Columbian 
has proved notably resistant. The amount of damage which may 
be done when nonresistant sorts are grown is commonly estimated 
at from one fourth to two thirds of the crop. The disease doubt- 
less spreads most rapidly during moist, warm 
summers, but its destructive effects upon the 
fruit crop are particularly noted during a sea- 
son of drought. 1 

The fungus. By the time that a cane is com- 
pletely wilted there may be found at the base 
of the wilted portion a short area dead and 
discolored, in which appear the pycnidia. When 

Fig. 174. CoNioTHY- expelled from the pycnidia the spores form 
RiUM FucKELii. (After , . , , 11111 1 

Stewart) brownish patches on the dead bark, or the 

dying canes might have a smutty appearance 
from the presence of numerous spores. Viewed singly the spores 
are very lightly colored, but in mass the brown color is pronounced. 
The spores measure 2.4-5 X 2-3.5 /^ (Fig. 174). Pure cultures of 
this fungus were obtained, but a description of growth characters has 
not yet appeared. Results from most carefully conducted inocula- 
tion experiments made from pure cultures have clearly demon- 
strated the parasitic nature of the disease, and the independence 
of Coniothyrium in producing it. 

1 Clinton thinks (Conn. Agl. Exp. Sta. Rept. (1906) : 321-324) that the raspberry 
cane blight fungus gains entrance through the flowers and young fruit, the spores 
apparently being spread by bees and other insects. In Connecticut the black 
cap varieties have been more susceptible, special complaint having been made of 
serious injury to the Parmer, Cumberland, and Kansas. It has also, however, in- 
jured red varieties and occurs on wild black raspberries in the same region. He 
presents no further proof of the connection with Leptosphaeria, but refers the 
fungus to that genus under the name Leptospharia Coniothyrmm (Fckl.) Sacc. 




, 



FUNGI IMPERFECTI 



;57 



Control. It appears that the only practical methods of prevent- 
ing this disease are to obtain healthy plants at the outset, to avoid 
planting where raspberries or other related plants have grown, and 
to remove and burn old canes as promptly as possible. The results 
with spraying have not thus far been successful. 



XLVIII. ROSE LEAF BLOTCH 
Actinoiiema Rosce (Lib.) Fr. 

Cobb, N. A. Black Spot of the Rose. Dept. Agl. N. S. Wales. Miscel. Publ. 

(2d Ser.) 666: 2-27. ///. 1904. 
SCRIBNER, F. L. Black Spot of Rose Leaves. U. S. Dept. Agl. Rept. (1887): 

366-368. pis. S, g. 

The rose leaf blotch, or spot, is perhaps the most common and 
injurious rose fungus aside from the powdery mildew (p. 224), This 
disease is characterized by more 
or less irregular brown spots, fairly 
well defined, on the upper sur- 
faces of the leaves (Fig. 175), 
varying from a few millimeters in 
diameter to areas covering more 
than one half the entire leaflet. 
In this darkened area there are 
distributed a small number of pyc- 
nidia, producing numerous, ellip- 
tical, two-celled, hyaline conidia. 
This spot may be controlled by 
the use of any standard copper 
spray, but it is not, of course, de- 
sirable to spray for a few weeks 
preceding the blossoming period. 
Control measures should there- 
fore look to preventing the dis- 
ease from securing a start previous to the blossoming season. 

There is considerable difference in the susceptibility of the dif- 
ferent host varieties. As a rule the bushy sorts are more severely 
injured and the climbing roses are often immune. If cuttings are 
selected from healthy plants, even susceptible varieties may be 
generally propagated with little fear of serious trouble. 



^x^ 




Fig. 175. Leaf Blotch of Rose 



358 FUNGOUS DISEASES OF PLANTS 

XLIX. LEAF SPOT OF THE PEAR 

Septoria Pyricola Desm. 

DuGGAR, B. M. Some Important Pear Diseases. Leaf Spot. Cornell Agl. 
Exp. Sta. Built. 145: 597-611. figs. 1^7-16^. 1898. 

The leaf spot of pear is a disease whicli may be readily dis- 
tinguished from the leaf blight subsequently described. It occurs 
throughout the eastern United States as an important fungus, both 




Fig. 176. Leaf Si'ot of Pear 

in orchards and nurseries. It is probably found throughout North 
America and is reported from various parts of Europe. 

The leaf spot fungus is confined to the leaves, and in orchards 
the chief injury to trees may be the reduced vigor for the next 
season, due to premature defoliation. It is rather remarkable that 
while seedling apple stock in a nursery may show leaf blight to a 
considerable extent, adjacent plots of budded plants may be seri- 
ously injured by the leaf spot. The budded stock of the second 
year usually suffers more severely, particularly since it is generally 
less cultivated after the first season. In the state of New York 
most of the standard varieties may be attacked. Bosc, Anjou, 
Clairgeau, Seckel, Bartlett, etc., may be considerably injured, but 
Flemish Beauty, Duchess, and Winter Nellis are more resistant. 



FUNGI IMPERFECTI 



159 



The Kieffer is practically exempt. In any case, however, the 
fungus may be readily controlled with Bordeaux. 

The spots on the leaves are few or numerous, angular, and the 
size varies greatly with the variety. Three fairly well differentiated 
zones of color are shown in an affected spot : at the center it is 
ashen gray, and within this area appear on either surface the minute 
pycnidia ; the next outer zone, or area, is brown, or black in very 
young leaves ; and surrounding this second there may be an area 




Fig. 177. Dilution Culture of Septoria Pyricola 

which is purplish in color (Fig. 176). These color details are lost 
in very old leaves, but the black papillae indicating the pycnidia 
then show up clearly. At maturity the spores may ooze out in dark 
uniform cirras. In cross section the pycnidium is clearly ovate in 
form. The wall is made up of several layers of dark cells, and the 
hyaline conidiophores arise from an inconspicuous inner layer 
(Fig. 178). The spores are flexuous and quite constantly two- 
septate, measuring about 60 X 3-4 /i. The mycelium is intercel- 
lular, brownish, and may be detected within the tissues at some little 
distance from the perithecium. The spores germinate readily in 



36o 



FUNGOUS DISEASES OF PLANTS 




Fig. 178. Sj-ptor/a Pyricola : Section of Pvcnidium 



nutrient media, 
germ tubes being 
pushed out from 
either end or from 
the middle (Fig. 
179). This fungus 
has been readily 
cultivated upon 
bean stems and 
pear twigs, and I 
have reported the 
growth as follows : 

Here the fungus 
grew slowly at first, 
producing after sev- 
eral weeks the pyc- 
nidia of the Septoria. 
After several trans- 
fers this fungus grows quite luxuriantly on bean pods or stems, as seen in fig- 
ure . . . , producing the pycnidia in a short time, and the pycnidia are then not 
so definite in form but formed of a 
very loose stromatic mass. The sub- 
merged hyphae are dark in color, while 
the aerial growth is dense and white, 
except the stromatic mass inclosing 
the pycnidium. I have had cultures 
for eighteen months ; and although 
they have been subjected to various 
climatic conditions, nothing of further 
interest has as yet come from them. 
In nature the fungus is being closely 
watched for other stages, but I can 
say nothing definite upon this point 
at present, although other fungi have 
been found on the old leaves. Imc. 179. Septoria Pyricola: Ger- 

minating Spores 
Control. This fungus has 

been readily controlled in the orchard by the use of standard Bor- 
deaux mixture applied as for pear scab. Where vigorous nursery 
stock would be produced, it is necessary to spray every season ; 
but a single application, after the first flush of growth, is often 
sufficient. 




FUNGI IMPERFECTI 36 1 

L. LATE BLIGHT OF CELERY 
Septoria Petroselini Desm., var. Apii Br. «S: Cav. 

Beach, S. A. Celery Septoria. N. Y. Agl. Exp. Sta. Built. 51: 1 37-141. 

1893. 
DUGGAR, B. M. Late Blight of Celery. Cornell Agl. Exp. Sta. Built. 132 : 

206-220. Jigs. ^S-60. 1897. 

Habitat relations. The late blight of celery is a comparatively 
recent disease in the United States, and in Europe it has not been 
considered a serious celery malady. It is most injurious as a rule 
during the early autumn, although a few spots of this disease may 
be seen at any time during the summer where it is at all prevalent. 
The spots are irregular in outline and of a rusty brown color. How- 
ever, when the conditions are most favorable for the development 
of the disease, the fungus may spread over the whole surface of 
the leaflets without the formation of characteristic spots. 

The late blight is destructive in the field until the plants are 
" lifted." It may also extend its injuries to the storage coop or 
cellar. The conditions in the storage cellar may be, during warm 
days of early winter, most favorable for the spread of the fungus. 
In a moist, poorly ventilated cellar I have found the pycnidia of 
this fungus over the surfaces of entire leaves, and the whole plant 
wilted as a result. 

The fungus. The pycnidia of this fungus are evident soon after 
the spots turn brown, — as dark papillae more or less in the center 
of the affected areas. The spores are slightly curved and septate, 
the septa being usually readily seen only by the use of stains. 

Fresh spores germinate in a few hours in nutrient agar, and 
transfers may be made to bean stems and any other solid media 
for a more profuse mycelial development. Moreover, on solid 
media mature pycnidia may be secured within a few weeks. They 
develop superficially, and are then composed of loosely woven 
brown hyphae. The mycelium is entirely distinct from that of 
Cercospora Apii. 

Control. In the field Bordeaux or ammoniacal copper carbo- 
nate may be used as a spray, but in the storage cellar it is necessary 
to pay special attention to all matters of sanitation. When the 
disease is abundant in the field, additional risk is taken, of course, 
by placing the crop in storage. 



362 



FUNGOUS DISEASES OF PLANTS 



LI. SEPTORIA: OTHER SPECIES 

Septoria Lycopersici Speg., leaf blight of the tomato. The 
tomato is attacked by several leaf fungi which may become destruc- 
tive, and of these fungi the one most injurious throughout the 
range of tomato culture is the organism causing what is known as 
leaf blight. The leaves are the parts most severely affected, and on 
these parts appear numerous small angular spots pale in the centers 



rm 




V:i--- 




/ 


■JJl^. 






WBHBWIii-^^a^ii^. -"^9 


^^^^k, 


' mK 




^^^^^K^ 




Jfef«* ■«*^tl 


m 


. ■ ;;■ ■:;:■' ^ :;"'^-\^-'% 


Bf 




f'i4 




. v'-«^PH|| 


^gplB 


i ■ 




^M 



Fig. i8o. Tomatoes defoliated by the Leaf Blight Fungus 
(Photograph by IL H. Whetzel) 



and with colored borders. The affected leaves have a tendency to 
curl dorsally throughout their length, eventually drying and falling. 
Petioles and twigs may also be affected, and small, elongate, dark 
spots may appear on the fruit. 

The pycnidia are found on the upper surfaces of the leaves in 
the larger spots. It is probable that the fungus passes the winter 
in the old leaves and other refuse. 

The use of Bordeaux mixture during the early part of the 
season has generally resulted in successful prevention. 



FUNGI IMPERFECT! 



0^0 



Septoria Ribis Desm.^ is common upon various species of Ribes. 
With respect to the economic hosts many varieties of both currants 
and gooseberries are subject to attack. Large spots with pale 
centers and brown borders are produced (Fig. i8i). These are 
readily distinguished from those produced by the anthracnose (cf. 
Fig. 79) by the large size, the well-defined outline, and the pale 
central dead area. The pycnidia are found in small groups at the 
centers of the older spots. 
They are subspherical, and, 
when approaching maturity, 
crowded with spores arising 
from short filiform conidio- 
phores. The conidia are long- 
filiform and measure 50-60 x 

3-4/^- 

Septoria Rubi West pro- 
duces numerous small spots, 
usually pale in the centers with 
colored borders, on the leaves 
of various species of Rubus, 
both blackberries and rasp- 
berries.^ The fungus has been 
reported from many sections 
of the world, and is doubtless very generally distributed. Pyc- 
nidia are developed in the center of the larger spots, and these 
give rise to long tapering spores, 40-50 /x, ordinarily twice or 
more septate by rather indistinct divisions. 

Septoria consimilis F. & M. The lettuce leaf spot, caused by 
this fungus, is prevalent on garden lettuce, particularly during the 
latter part of the season. It is perhaps the chief " spot " fungus 
of this plant, but may be held in check by the immediate destruc- 
tion of the discarded and seeded plants in the field at the close of 
the season. 

Septoria Dianthi Desm. produces small brown spots upon the 
leaves and internodes of the carnation. The leaves are often bent 

^ Pammel, L. II. Spot Diseases of Currants and Gooseberries. Iowa Agl. Exp. 
Sta. Built. 13: 67-70. figs. 15-16. 1891. 

2 Ohio Agl. Exp. Sta.' Built. 4 (6) : 126. 1891. 





J^ 




\ 


^^E^HE^^^K 






i 


f 



Fig. 181. Lkaf Spot of Currants 
(Photograph by F. C. Stewart) 



3^4 



FUNGOUS DISEASES OF PLANTS 



or distorted. This disease is not likely to be serious where proper 
ventilation and subirrigation are provided for. 

Septoria Chrysanthemi Cav. may become a serious pest upon 
the maturing leaves of the cultivated chrysanthemum. 



LII. CURRANT CANE BLIGHT 

DothiflreJIa 

This disease appears to be most abundant in the Hudson 
Valley in New York. It has, however, been found in other 
sections, though not destructive. The affected canes are wilted 
and killed during midsummer. The disease is probably more 

easily seen during a dry period on ac- 
count of the fact that when the water 
supply is abundant, it may not be 
noticeable during the growing season. 
The fungus producing this disease has 
been isolated from both the diseased 
wood and pith, and upon infection is 
capable of reproducing the disease. Sev- 
eral fruiting stages have been found, at 
least one of which is unquestionably a 
stage in the life cycle of this fungus. It 
has been difficult to identify all of the 
spore forms with certainty, but the pyc- 
nidial stage would be considered a species 
of Dothiorella (Fig. 182). Successful 
infection experiments with mycelium 
obtained from germinating pycnospores 
have been made. The relationship of 
this fungus to an ascogenous stage 
sometimes associated with it, or follow- 
ing it, upon the dead canes has been 
under careful study, but has not yet 
been reported. The fungus grows read- 
ily upon any of the solid nutrient media, 

V,,. Q T-> producing a considerable gray-green 

riG. 162. Dothiorella ON ^ *=> fc> .7 & 

Currant Canes mycelium. 




FUNGI IMPERFECTI 



365 



LIII. LEAF BLIGHT OF PEAR AND QUINCE 
Entomosporimn maculatum Lev. 

DuGGAR, B. M. Some Important Pear Diseases. II. Leaf Blight. Cornell 

Agl. Exp. Sta. Built. 145: 611-615. 1898. 
Fairchild, D. G. Experiments in Preventing Leaf Diseases of Nursery 

Stock in Western New York. N. Y. Agl. Exp. Sta. Kept. 11 : 642-652. 

1892. (Also, Journ. Myc. 8: 338-351.) 
SCRIBNER, F. L. Leaf-Blight and Cracking of the Pear. U. S. Dept. Agl. 

(1888): 357-364- 

Habitat relations. The leaf blight of the pear and quince has 
been observed in this country as well as in Europe for many years ; 
it has also received considerable attention at 
various agricultural experiment stations in pear- 
producing regions. In New York it is most 
abundant apparently in the Hudson Valley, and 
in general it would seem to be more injurious 
in states in the Appalachian region. Nearly 
all varieties of pear are affected, but Duchess 
and Kieffer are perhaps the most resistant of 
those ordinarily grown. Moreover, in different 
regions of the Atlantic states there seems to be 
a difference in the susceptibility of varieties. 
Considerable damage may also be done in the 
nurseries to seedling pears, although grafted 
stock is far more subject to the leaf spot than 
to the leaf blight. Root suckers on seedling 
pears throughout the country are very generally 
injured. The spots are sometimes noticed on 
the tips of young branches, and it has been very definitely shown 
that in such situations the fungus may readily pass the winter. 
The effect of the disease upon seedlings is to harden the wood 
early and prevent the best results from budding. 

Symptoms. The spots produced by this fungus are particularly 
evident on the upper surfaces of the leaves, occurring first as small 
discolored areas which become dull red at the center, with dark 
borders. They are more or less circular in outline, but they may be 
closely clustered and considerably confluent. In severe attacks the 
leaves may become yellow or brown, and they readily fall. This 




Fig. 183. Entomo- 

spoRiuM ON Pear 

(Photograph by 

Geo. F. Atkinson) 



i66 



FUNGOUS DISEASES OF PLANTS 



1 




disease is distinguished from the leaf spot by smaller spots more 
colored when young and more nearly circular. They are also 

less clearly defined on the under 
surfaces. 

The blight also attacks the fruit. 
In this case the spots are at first 
red but later darker in color. The 
drying of the surface layers accom- 
panying the effects of this disease 
may cause a cracking very much 
as in the case of pear scab. 

The fungus. The larger spots 
of the leaf blight will generally 
show at the time of leaf fall one 
dark papilla in the center of each. 
This papilla is an indication of 
an acervulus, or spore-producing 
stroma. The mycelium from which 
this stroma originates penetrates 
the epidermal layer and also to 
some extent the hypodermal tis- 
sues, and the affected region shows a general collapse of the 
cells. From the subcuticular stroma there are produced on minute 
conidiophores numerous "insect-like" spores (Figs. 185, 186). The 
spores germinate readily and the fungus is thereby spread during 
the same season. _ 

Various authors .>-<^.,,-(^,'>j//j,/,f^i"A- - i.. , ^, \ 

have described what 

is supposed to be a 

perfect stage of this 

fungus. Sorauer^ 

has referred the 

ascogenous stage to Stigmatca Alcspili. Atkinson '^ has found this 

fungus on wintered leaves of the quince and has considered it to 

be a member of the genus Fabraea. 

Control. Experiments upon nursery stock have shown that 
Bordeaux mixture of any 'Standard strength may be used success- 
1 Pflanzcnkrankheiten, /. c. (cf. p. 371). 2 Garden and Forest 10 : 73-74. 1S97. 



Fig. 184. Entomosporium on 

Quince. (Photograph by H. H. 

Whetzel) 




FUNGI IMPERFECTI 



367 



fully as a preventive. Five or more 
sprayings have been profitable upon 
American, French, and Japanese 
stocks, although this has not afforded 
complete protection. Spraying as for 
the pear scab is advised when this 
disease becomes a matter of suffi- 
cient economic importance in the 
orchard. 




In;. I.S6. SroKKs of thk 

EnI'UMOSI'OKIUM 



Liv. SOOTY i;lotch and fly speck of the apple and 

OTHER PLANTS 1 

I.cptotJiyriiii)i J\)»ii (Mont. & Fr.) Sacc. 

Clinton, G. P. Notes on Parasitic Fungi. Fly Specie. Sooty Blotch. Conn. 

Agl. Exp. Sta. Rept. (1903): 299-302. 
Powell, G. H. A Fungous Disease of the Apple. Garden and Forest 9 : 

474-475- 
Selby, a. D. Sooty Fungus and Fly Speck Fungus. Ohio Agl. Exp. Sta. 

Built. 79 : 133-134. 
SxuRcas, W. C. On the Cause and Prevention of a Fungous Disease of the 

Apple. Conn. Agl. Exp. Sta. Rept. 21 : 1 71-175. 

According to the unpublished observations of Floyd the sooty 
blotch and fly speck are apparently stages of the same fungus. 
They are almost invariably associated upon the host (Fig. 187), but 
may occupy distinct areas upon the same portion of the plant. 
They seem to occur upon the fruit of the apple throughout the 
limits of its culture. A sooty blotch and a fly speck are also found 
upon the pear, and along a roadside near Columbia, Mo., there 
were found more than twenty-five hosts affected by what was 
apparently the same fungus. These plants were all woody in tex- 
ture, and the fungus occurred generally on the younger twigs 
and petioles. The forms upon these hosts may be provisionally 
referred to as one fungus. Observation indicates that the organ- 
ism is most abundant under conditions of considerable moisture, 
half shade, and abundant dust. The market value of apples is 
affected by the discolorations which result. 

1 For the material of this account I am very largely indebted to unpublished 
data kindly furnished by Mr. K. F. Floyd of the Fla. Exp. Sta. 



568 



FUNGOUS DISEASES OF PLANTS 



^ 




>»<*^ 




The mycelia of both the blotch and the speck are superficial, at 
most merely roughening the surface of the cuticle. The blotches 

are irregular in 

outline, sometimes 

^^^^^^ coalescing into 

'^lir^SI^-.-.vv^^x^^^K^"- *^^»■ large areas. The 

specks, as the name 
^Vi-'^v^-^ • ' indicates, are small, 

•■ v:':^' ' -:- circular, dark col- 

, ■' ■ -. . ' « ored flecks associ- 

ated in groups, and 
sometimes distrib- 
uted over large 
■4^ ^^eas. 
^/ A network of ra- 

diating olive-brown 
or fuliginous hyphas 
made up of more or 
less barrel-shaped 
cells constitute the 
On the 




i^ 



Fig. 187. Fly .Speck and Sooty Blotch of Apple 



blotch. Cell fusions and cell aggregations are common 
other hand, the specks are 
at first dense aggregates 
of rather light colored hy- 
phae, and from such specks 
delicate hyphae may be 
traced to similar neighbor- 
ing spots or to blotches. 
A mature speck becomes 
shining black and dry. 
Then the central portion 
breaks away and is pre- 
sumably the source of new 
infections. No spore form 
has been found accom- 
panying this phase. Both 

, ''^^ r r 1 Fig. 188. Leptothyrwm Pomi: Develop- 

types 01 fungus have, ^ „ 

J ^ ° ' MENT OF PyCNIDIA FROM PyCNOSCLEROTIA 

however, been followed (Photograph by B. F. Floyd) 




FUNGI IMPERFECTI 369 

throughout the autumn and winter and careful sections made at 
different times. In the case of the blotch, as the season advances, 
the cell aggregates may develop a definite sclerotial-like body 
(November in Missouri). By March this body has differentiated 
into a pycnidium (Fig. 188) 25 to 100 /x in diameter, of the 
Leptothyrium type, bearing hyaline, elliptical spores. The latter 
measure 12-14 X 2-3/^. 



CHAPTER XIII 

HEMIBASIDIOMYCETES 

I. USTILAGINALES 

Brefeld, O. Die Brandpilze, I. Unters. a. d. Gesammtgeb. *d. Mykologie 5 : 

I -220. pis. I -13. 1883. 
Brefeld, O., u. Falck, R. Ibid. 13: 1-75. pis. 1-2. 1905. 
Clinton, G. P. North American Ustilagineas. Proc. Boston Soc. Nat. Hist. 

31 : 329-529. 1905. 
Dangeard, p. a. Recherches histologiques sur la Famille des Ustilagin^es. 

Le Botaniste 3 : 240-281. 1892. 
De Bary, A. Die Brandpilze. 144 pp. 8 ph. 1S53. 
DiETEL, P. Ustilagineae und Tilletiineae. Natiirl. Pflanzenfam. (Engler u. 

Prantl, Red.) 1 (Abt. i **): 2-24. figs. 1-13. 
Fischer de Waldheim, A. Beitrage zur Biologie u. Entwickelungsges. d. 

Ustilagineen. Jahrb. f. wiss. Bot. 7 : 61-144. pis. 7-12. 1870. 
Harper, R. A. Nuclear Phenomena in Certain Stages in the Development 

of the Smuts. Trans. Wis. Acad. Sci., Arts, and Letters 12: 475-498. 

pis. 8-g. 1899, 
Plowright, C. B. a Monograph of the British Uredineae and Ustilagineas. 

347 pp. 8 pis. 1889. 
Tulasne, L. R. et C. Memoire sur les Ustilagindes compardes aux Uredi- 

nees. Ann. d. Sci. Nat. (Bot.) 7 (3 S^r.): 12-127. pls. 2-y. 1847. 

The Ustilaginales, commonly known as the " smut fungi," repre- 
sent, in the opinion of most mycologists, what may be considered 
the lowest of the basidium class. Without exception, they are 
parasitic fungi, and they occur upon herbaceous flowering plants. 
Many species infect grasses. There are, however, thirty-five 
families of host plants in North America alone, representing 
(according to Clinton) one hundred and sixty-four genera and 
four hundred and forty-two species. 

The method of infection is diverse. In a few species infection 
is apparently limited to the germinating seedlings, in many cases, 
however, taking place through any meristematic tissues. The 
mycelium may extend throughout the entire plant or it may be 
located in limited areas, sometimes being confined to particular 
organs of the plant. It is commonly intercellular, frequently 
developing haustoria. Upon the production of spores it may 
disappear by a gelatinization process. Reproduction is seldom by 

370 



HEMIBASIDIOMYCETES 37 1 

means of conidia produced on the external portion of the host, as 
in Entyloma, and typically by means of chlamydospores formed 
within interstitial or terminal cells or hyphae. Chlamydospores are 
for the most part dark colored, simple or agglutinated, and with or 
without sterile appendage cells. The chlamydospores produce upon 
germination a basidium-like structure known as a promycelium, 
which in turn originates lateral or terminal sporidia. In this order 
the fusion of sporidia, or of germ tubes from these, is common. 
This cell fusion is not accompanied by nuclear fusion. Each 
sporidium is provided with a single nucleus. 

This order is divided into two families, Ustilaginaceae and 
Tilletiaceas, based upon characters which become evident only in 
germination. The characters are therefore largely those of the 
germ tube or promycelium. 

Ustilaginaceae. Spore masses are made up of simple or com- 
pound spores. The promycelium is usually divided into two or 
four cells, originating both lateral and terminal sporidia, which 
sporidia, in saccharine or other nutrient solutions, are for the most 
part able to bud after the fashion of yeast fungi for an almost 
indefinite period of time. This family includes from seven to 
eleven genera, according to different authorities. 

The characters of only three genera need to be considered in 
order to become familiar with the basis of classification. 

1. Spores single, spore masses dusty at maturity and without any sort of 

inclosing membrane Ustilago 

2. Spores agglutinated in balls, spore masses more or less dusty. Spore 

balls usually evanescent, spores very dark Sorosporium 

3. Spores agglutinated in balls, spore masses more or less dusty. Spore 

balls rather permanent, spores now adhering by folds or thickenings 
of the outer coat Tolyposporiiiin 

Tilletiaceae. Spore masses are made up of simple or compound 
spores ; these masses dusty and exposed, or imbedded in the tis- 
sues. The promycelium is short, originating usually an apical clus- 
ter of more or less filiform sporidia. The latter may fuse in pairs, 
and whether fusing or not, may produce secondary conidia, or may 
germinate directly into infection hyphae. 

This family includes from eight to ten groups of generic rank, 
the differentiated characters of three of which may be indicated. 



372 FUNGOUS DISEASES OF PLANTS 

1. Spores single, spore masses dusty, spores without conspicuous tube-like 

hyaline appendage Tilleiia 

2. Spores single. Spores in loose groups, imbedded in the tissues. Entyloiua 

3. Spores agglutinating in balls, spore masses dusty, spore balls invested 

with a cortex of sterile cells Urocystis 



1 



II. LOOSE SMUT OF OATS 
Ustilago Ave/ice (Pers.) Jens. 

Jensen, J. L. Om Kornsorternes Brand. Copenhagen, 1888. 

Kellerman, W. a., and Swingle, W. T. Loose Smut of Cereals. Kansas 
Agl. Exp. Sta. Rept. 2: 213-288. pis. i-g. 1890. 

Kellerman, W. A., and Swlngle, W. T. Additional Experiments and Ob- 
servations on Oat Smut. Kan. Agl. Exp. Sta. Built. 15: 93-133. 1890. 

Stuart, W. Formalin as a Preventive of Oat Smut. Ind. Agl. Exp. Sta. 
Built. 87: 1-26. 1 90 1. 

Swingle, W. T. The Grain Smuts. U. S. Dept. Agl. Farmers' Built. 75 : 
1-20. T^'Vj". 1-8. 1898. 

The loo.se smut of oats is one of the most common and destruc- 
tive of the smut family. It is found wherever oats are cultivated, 

and it would not appear that 
climatic conditions influence 
materially the abundance of 
the fungus. Besides the vari- 
ous varieties of the cultivated 
oats {Ai'ena sati^'a), it has only 
been reported upon Avcjia 
fatJM, the latter in California. 
Like most of the other 
loose smuts of grain, it ma- 
tures at or about the time the 
grain is in flower, and dur- 
ing the ripening season it is 
widely distributed. The gen- 
eral appearance of the loose 
smut is striking, and usually 
as shown in Fig. 189. It has 
been estimated that the aver- 
age loss to the oat crop 
throughout this country may 
. 189. Loose Smut of Oats be placed at about eight 




HEMIBASIDIOMYCETES 



173 



per cent. This estimate would mean a loss of about twcnt)' million 
dollars, based upon the statistics of oats produced during 1906. 

The mycelium of the oat smut is present throughout the tissues 
of the affected plants. Infection takes place by means of the germi- 
nating conidia at the time of germination of the seed. The mycelium 
branches abundantly in practically all tissues of the developing 
flowers, completely infesting the young ovule and the inclosing 
floral structures. The mycelium, at the time that spore, formation 
becomes evident, shows a nodulate appearance, and the branches 
are closely fascicled, like clusters of grapes. Within each swollen 
area of the mycelium a chlamydospore is found. As the chlamydo- 
spores mature, the inclosing walls of the parent hyphae and much 
of the general mycelium which is not differentiated into spores 
gelatinizes or otherwise breaks away, and the spores are set free 
in large masses. With the increased growth of the mycelium and 
the formation of spores, the softer cells of the host plant are rapidly 
absorbed, so that at maturity only the more resistant tissues of the 
florets may remain, the whole ovule with its inclosing glumes being 
largely converted into the dusty mass of sooty spores. In a closely 
related species of oat smut {Ustilago levis), long regarded merely 
as a race or variety of Ustilago Avencs, the mycelium destroys only 
the kernels and does not attack the glumes. The smut therefore 
remains inclosed or hidden. 

The spores are almost spherical or slightly ovoidal, and echinu- 
late, varying in length from 5 to 9 /tt. They are also olivaceous 
in color, with a lighter area at one side. Germination of the fresh 
or of preserved spores may be readily secured. In fact, in herbarium 
material spores may preserve their vitality for several years. Ger- 
mination may proceed in pure water or in nutrient solution. 

The promycelium is frequently four-celled, though somewhat 
variable in this regard, and it often assumes abnormal forms, as 
shown in Fig. 190. The conidia are produced laterally and termi- 
nally. They are elliptical or subelliptical in form and measure 
4.5-8 X 4.5-6 /i. In nutrient solutions the well-known budding 
of the conidia may continue almost indefinitely, and under certain 
conditions, or after extensive cultivation, mycelium-like cells may be 
produced. Upon the living host, however, the conidia germinate 
by the production of an infection hypha. 



374 



FUNGOUS DISEASES OF PLANTS 



\ 



Control. In an endeavor to control smut in oats, bunt in wheat, 
and other more or less similar diseases, a careful study has been 
made of a variety of fungicides or toxic agents in solution, and of 
hot water. 

The hot water treatment of the seed grain is the method in 
more common use. This method consists in immersing for ten 
minutes in water at a temperature of from 132° to 133° F. It has 
been found desirable to put the seeds into a basket or perforated 
tin vessel, and this may be previously dipped into warm water at a 
temperature of about 110° to 120° F., in order that the tempera- 
ture of the hot water may not be greatly reduced by using cold 
seed. The water in which the seeds are finally immersed should 

be retained during 
the ten minutes at 
a temperature of 
not less than 130°, 
otherwise additional 
warm water should 
be added during the 
process. Further- 
more, it is desirable 
to throw the seed 
into cold water be- 
fore treatment, so 
that the smutted 
seed may be floated and skimmed off, for the treatment would be 
of small value if the large quantity of spores still held within the 
kernels of smutted grain were not removed. The hot water method 
is effective, but since it appears somewhat complicated, it is now 
being superseded by a formalin treatment. In its simplest terms 
the latter consists in dipping the seed in a solution containing 
I pint of formalin to 30 gallons of water. The seed may be put 
into sacks or baskets of from ^ to i bushel each, and, as before, 
immersed in the barrel of formalin solution for about ten minutes, 
drained, put away wet in the sacks, or heaped and covered for two 
hours and finally spread out to dry rapidly before danger of germi- 
nation. Shoveling over will facilitate the drying. Copper sulfate, 
potassium sulfide, and other germicides have also been employed. 




Fig. 190. UsTiLAGo Avenai: Germinating Stores 



HEMIBASIDIOMYCETES 2>7^ 

III. LOOSE SMUT OF WHEAT 
Usfilago Tritici (I'ers.) Jens. 

Brefeld, O., u. Falk, R. Unters. 13 : /. c. (Die Bluteninfektion bei den 

Brandpilzen). 
Freeman, E. M., and Johnson, EL. C. The Loose Smuts of Barley and 

Wheat. Bur. Plant Ind., If. S. Dept. Agl. Built. 152: 1-43. pis. 1-6. 

1909. 
Swingle, W. T. The Grain Smuts, /. c. (see Ustilago Avence). 

The above species, producing the well-known loose smut of 
wheat, is almost as widely distributed as the organism producing 
the loose smut of oats. The general appearance of the affected 
plant at the time of flowering is much the same as in the case of 
oats, and in many respects the life histories of the two species are 
similar. This species is found upon practically all varieties of wheat 
and under all climatic conditions. Morphologically, this fungus is 
scarcely to be distinguished from the oats smut, and this is true 
whether one considers the form of the spores or the characters 
made evident upon germination ; but the absolute failure of cross 
inoculations indicates that the two forms are distinct. According 
to recent investigations, moreover, it would appear that this species 
may also gain entrance to the host plant at the time of flowering. It 
is stated that the infection tube penetrates the stigma and style, and 
by that means enters the developing seed. In the developing seed 
it retains its vitality and grows up through the plant when the seed 
germinates. This mode of infection is said to be the most com- 
mon ; therefore, according to these results, treatment of the seed 
wheat for loose smut might seem to be useless ; nevertheless, from 
experiments which have been made in this country, it would seem 
that a modified method of Jensen's hot water treatment is partially 
effective against this fungus. It appears at present possible to assign 
a cause for this latter fact. It does not seem to be due to a greater 
number of infections through seedling stages than is now assumed, 
and is presumably due to the killing of the fungus within the tissues 
by the hot water method. 

Control. In view of the recent studies upon blossom infection, 
it would seem that the only reliable means of prevention would 
consist in the hot water treatment together with seed selection. 
It would be necessary to select seed from a field free of smut. 



Z1^ 



FUNGOUS DISEASES OF PLANTS 



Where the disease is very abundant it would be practicable, on 
plats to be employed for seed, to weed out smutted plants prior to 
final maturity. The most recent recommendation with respect to 
seed treatment is to soak five hours in cold water, and then ten 
minutes in water at 54° C. 



IV. SMUT OF CORN 
Ustilago Zecc (Beckm.) Ung. 

Arthur, J. C, and Stuart, W. Corn Smut. Ind. Agl. Exp. Sta. Ann. Kept. 

12: 84-135. 1900. 
Hitchcock, A. S., and Norton, J. B. S. Corn Smut. Kan. Agl. Exp. Sta. 

Built. 62: 169-212. pis. I -10. 1896. 
Knowles, E. L. a Study of the Abnormal Structures Induced by Ustilago 

Zeae-mays. Journ. Myc. 5: 14-18. pis. 2-y. 1889. 

The common smut of corn {Zca mays) 
occurs in all regions where maize is grown. 
It is productive of considerable losses at 
times, and it is probable that in many corn- 
growing sections the yearly loss will aver- 
age as high as 5 per cent. It may vary, 
however, from o to about 25 per cent. 

Habitat relations. This fungus some- 
times causes enormous enlargements of 
various parts of the host, occurring in 
staminate and pistillate flowers, on the 
stalk, especially at the nodes, and also in 
the leaves. The abnormalities or swellings 
are usually prominent and often attain the 
size of several inches in diameter. Very 
careful experiments throughout a long 
period of time have made it clear that 
infection takes place through any young 
and growing tissue, but that the plant is 
not affected, as a rule, until a foot or 
more in height. The spores retain their 
vitality in the soil for some time, and the 
sporidia may, by a sprouting process, be propagated and dissem- 
inated through manure or compost spread upon the land. The 




Fig. 191. Ustilago Ze.e. 
Smut of Corn 



HEMIRASIDIOMYCETES 



177 



mycelium is rather sixirsely distributed throughout the general area 
of normal tissue, from which swellings arise, but it becomes devel- 
oped at certain points in quantity in the form of pockets, in which 
areas it is later differentiated into the spores. Upon the stem the 
abnormal growth has been 
found to originate principally 
just beneath the epidermis, 
that is, outside of the area 
of the fibrovascular bundles. 
Rapid multiplication of the 
host cells occurs, and these 
become diverse and always 
abnormal in form. Neighbor- 
ing bundles send branches 
into the abnormal tissue, and 
the bundles at some little dis- 
tance may also show consider- 
able variation from the normal 
type. At maturity cells of the 
host are very largely broken 
down, and the pockets of 
spores are surrounded by a 
membrane made up of modi- 
fied fungous threads mingled 
together with dried host cells. 
This membrane is soon broken 
and the loose spores are set 

free. The spores are more or less spherical, though sometimes 
irregular, measuring often 8-12 yu., and the walls are beset with 
blunt echinulations. The spores germinate readily in water or in 
nutrient solutions in the normal manner. This fungus is known 
only upon one host besides the corn, that is, EucJiUena luxnrians. 
One other species of smut is found upon the corn, Ustilago 
Rciliaiia, but this is readily distinguished from the common smut. 
Control. Since this fungus may gain entrance to the host at 
any time, prevention consists in cutting out the affected stalks 
before the spores mature. Such stalks, moreover, should be 
destroyed and not thrown upon the compost heap where the 




Fig. 192 



Ustilago nuda: Loose Smut 
OF Barley 



378 FUNGOUS DISEASES OF PLANTS 

fungus will multiply itself and be returned to the land in a form 
to do considerable damage to the crop the following season. It is 
commonly stated that fields heavily fertilized with barnyard manure 
develop a higher percentage of smutted corn. 



V. SMUT OF BLUE-STEM GRASS 

Sorosporium Syntherismic (Pk.) Farl. 

For the most part, the various species of Sorosporium occur 
upon the so-called blue-stem and poverty grasses, belonging to the 
genus Andropogon and Aristida. Several species are therefore 
common but of slight economic importance. Sorosporinin Synthc- 
risnue is found, however, upon several species of Panicum and 
Cenchrus, and is quite widely distributed throughout the United 
States. The sori are usually confined to the inflorescence, the 
whole of which may or may not be affected. At maturity they are 
inclosed in a false membrane, somewhat similar to that in Ustilago 
ZecB, which ruptures, exposing the spore masses and shred-like 
remnants of host tissue. The spores adhere together in spore balls 
for a relatively short time, the balls being usually variable in shape, 
measuring from 50 to 100 /x in length. The spores are spheroidal 
or irregular in outline, measuring 9 to 1 3 /*, and they are covered 
with minute wart-like projections. 

VI. TOLYPOSPORIUAI P>ULLATUM (Schroet.) Schroet. 

The above species is probably the most widely distributed of 
this genus in the United States. It occurs upon the common barn- 
yard grass {EcJiinocJiloa cnisgalli). The sori are confined to the 
ovule sacs, and, as in the preceding species, they are covered with 
a membrane which upon being ruptured exposes the spore balls. 
The latter are from 50 to \6o \x. in length, black and opaque, con- 
sisting of one hundred or more closely united spores. The spores 
appear flavous or reddish brown. According to Clinton they are 
" covered with a thin, tinted, outer coat, more or less folded in 
ridges, by which the spores are bound together, and which, on the 
rupturing of the spore balls, often show as spiny projections at the 
spore margins, usually ovoidal, spherical, or polyhedral, 7 to 12 /a," 



HEMIBASIDIOMYCETRS 379 

VII. BUNT, OR STINKINC; SMUT OF WHEAT 
Tillctia faicns (B. & C.) Trel. 

Kellerman, W. a., and Swingle, W. T. Preliminary Experiments with 
Fungicides for Stinking Smut of Wheat. Kan. Agl. Exp. Sta. Built. 12 : 
27-50. pi. I. 1890. 

Kellerman, W. A. Second Report on Fungicides for Stinking Smut of 
Wheat. Kan. Agl. Exp. Sta. Built. 21 : 47-72. 1891. 

Distribution and symptoms. The above species is the more 
commonly distributed smut of this family upon grain in the United 
States, and while very commonly found in greater or less abun- 
dance, it is nevertheless entirely absent from some considerable 
wheat-growing regions. On the other hand, in portions of the 
Northwest, and extending also into Canada, there are regions in 
which the losses from this fungus have amounted to from one half 
to two thirds of a crop. The fungus affects the various varieties of 
wheat, but is not found upon any other grain. Little definite infor- 
mation, however, has accumulated concerning the susceptibility of 
different varieties to attack. The abundance of disease in certain 
regions would not seem to be greatly influenced by climatic con- 
ditions, but is probably very largely due to unfortunate practices in 
seed selection and to continuous cropping with wheat. The pro- 
duction of spores in the tis.sues of the host is confined very largely 
to the ovule sacs, at maturity the kernels being the chief seat of the 
spore masses. The spores are permanently concealed by the glumes 
which envelop the kernels ; but smutted heads are more or less 
recognizable on account of a slight difference in color and a some- 
what emphasized flaring habit of the spikes, due perhaps to slightly 
larger size of the infected kernels. The spores give rise to a pene- 
trating and disagreeable odor, which becomes very evident in the 
bin or during the milling process. In general, all of the kernels of 
a spike will be infested. 

The fungus. The spores are brown in color, usually oblong to 
spherical in form, with a smooth wall, varying considerably in size, 
extremes being more than from 16 to 25 /u. in length. The germi- 
nation of the spores of this species conforms well to the description 
given for the whole family. The acicular or needle-shaped sporidia, 
which are produced in the form of a crown on a short, continuous 
promycelium, frequently unite in pairs, and secondary sporidia 



380 FUNGOUS DISEASES OF PLANTS 

may be produced. Infection takes place through the young wheat 
seedhng, and the spores are very generally distributed by means 
of the seed. 

Control. Bunt of wheat has very generally been successfully 
treated by the methods recommended for oat smut. The formalin 
treatment is preferred. In applying this method, however, some 
prefer to sprinkle the wheat with the formalin solution (i pint to 
30 gallons) rather than to soak the seed. 

VIII. TILLETIA: (,)THER SPECIES 

Tilletia Tritici (Beij.) Wint. This species also occurs upon the 
wheat and was long considered to be merely a spiny or reticulately 
marked form of Tilletia ftvtcns. Experiments have demonstrated 
that the fungi are distinct. This species is less frequently found, 
but when present it produces practically the same effects as those 
described for the fungus last discussed. It sometimes occurs in 
conjunction with Tilletia fcvtcns. A microscopic examination per- 
mits an easy identification, since the reticulations on the wall of the 
spore are marked in this species. The spores are very nearly equal 
in size to those of the preceding and measure 16-22 /i in diameter. 

Tilletia horrida Tak. This fungus occurs in the ovaries of the 
cultivated rice, and it is now widely distributed in the United States 
as well as in the Orient. It is concealed by the enveloping blossoms 
and is not readily observed in the field. The spores are subspherical, 
measuring 22-33 /a in length. A band of scales 2-4/1,1 in width, 
due to the thickenings in the outer hyaline wall, is generally evident. 

Tilletia corona Scrib. This species occurs upon plants related 
to the rice, namely, members of the genus Leersia, and it is 
common upon these plants in their natural habitats in the south- 
ern states. 

IX. ENTYLOMA 

Entyloma Physalidis (Kalchb. & Cke.) Wint. The smut fungi 
of the genus Entyloma are not commonly productive of conspicu- 
ous deformities. In the case of Entjlovia Physalidis pale spots 
are produced upon the leaf of the ground cherry, or love-apple 
{Physalis pubeseens). The spores are intermediate in size, io-i6/i 
in length, and they are situated in small masses, or beds, scattered 



HEMIBASIDIOMYCETES 381 

throughout the affected areas. They are light in color, often nearly 
hyaline. The distribution of the spores is only effected by disinte- 
gration of the leaf. There are, however, conidia in the life history 
of some species of this genus of smuts. In this species they are 
scolecosporic in form, 30-55 x 1-2 fx. No very serious diseases 
of cultivated plants are induced by species of Entyloma, although 
the genus is rich in forms. 

Entyloma compositarum h'arl. is widespread in the United States 
upon a variety of the composites, including among these species 
of Ambrosia, Aster, Erigeron, etc. The minute sori occur in the 
leaves. The spores are subspherical or ovoidal, 9-14 At, and hyaline. 
The under surfaces of the leaves may be profusely covered with 
the conidial form, which is in this case like a species of Cercospo- 
rella with relatively short spores and conidiophores. The conidia 
are fusiform or slightly clavate and measure 15-20 x 2-3 /x. 

Entyloma Ranunculi (Bon.) Schrot.^ is found upon various 
species of Ranunculaceae. The life history of this form has been 
carefully studied. 

X. ONION SMUT 

CTocysfis Ccpiihc Frost 

Selby, A. D. Onion Smut. Ohio Agl. Exp. Sta. Built. 122 : 71-84- fig^- 

J, 4. 1900. 
SiRRiXE, F. A., and Stewart, F. C. Experiments on the Sulphur-Lime 

Treatment for Onion Smut. N. Y. Agl. Exp. Sta. Built. 182: 145-172. 

1900. 
Sturgis, W. C. Transplanting, as a Preventive of Smut upon Onions. Conn. 

Agl. Exp. Sta. Rept. 19 : 176-182. 1895. 
Thaxter, Roland. The " Smut" of Omon?,{Urocystis CepiihT). Conn. Agl. 

Exp. Sta. Rept. (1889): 129-153. ph. 1-2. 

Habitat relations. The onion smut has been known as an 
important disease-producing organism in the United States for 
about forty years, the first published notes of its effects being 
in the reports of the Massachusetts State Board of Agriculture, 
1869 to 1870. The fungus seems to be of American origin and 
its injuries are very largely confined to the eastern states, particu- 
larly New England. It occurs, however, as far west as Indiana, 
It would not appear that climatic conditions affect the prevalence 

1 Ward, H. M. On the Structure and Life History of Entyloma Ranunculi 
(Bon.). Phil. Trans. Royal See. London. 178 B : 173-185. /A. j, /. 1887. 



382 



FUNGOUS DISEASES OF PLANTS 



of the organism, nor does it seem that soil conditions are of any 
great importance. The host frequently shows the presence of the 
fungus soon after the first leaf appears. Dark spots are usually 
first noticed just below the knee of the first leaf, and these are 
frequently repeated in the leaves subsequently formed. The 
whole plant may therefore be very largely infected, although in 

exceptional cases 
the fungous my- 
celium seems to 
have directed it- 
self into the first 
leaf and disap- 
peared upon the 
withering of this 
organ. Soon 
after the spots 
are noticed upon 
the leaves longi- 
tudinal rifts are 
formed, and 
there are ex- 
posed threads 
of fibrous tissue, 
together with 
quantities of a 
granular spore 
powder, which 
latter consists of 
the characteristic 
spore masses or 
balls. Fig. 193, rt: 
shows an onion 
with a character- 
istic form of disease. The spore balls are washed into the soil, 
if diseased bulbs are not promptly removed, and the soil is un- 
questionably the chief source of the annual infection. It is 
possible that the spores may also adhere to the surfaces of 
the seed and thus further disseminate the fungus. 




Fig. 193. Urocystis, General Characteristics 
(a, l>, and c, after Thaxter) 

a, b, and r, Urocystis Cefuhe ; if, Urocystis occulta 



HKiMl IJASIDK )MYCKTES t^St, 

The fungus. It has been ascertained, apparently beyond doubt, 
that the spores may often retain their capacity for germination 
in the soil for a period of twelve years. The spore balls are more 
or less spherical in general outline and vary from 17 to 25 /x in 
greatest diameter. The spores in a ball may number several, but 
frequently only one is present. The sterile cells, which usually 
form a complete envelope, are slightly colored, generally sub- 
spherical in form, 4-8 /x in length. The germination, which has 
been carefully figured, commonly conforms to that of this family 
of fungi (Fig. 193, /;). 

Control. Since infected soil is the chief source of trouble, 
it is practically useless to treat the seed. The most effective 
method of prevention is that of transplanting the seedlings, the 
seed having been previously sown in a bed of soil known to be 
free of smut. Since, however, transplanting is a laborious and 
expensive process, it is frequently desirable to treat the land 
or the drill in which the seed are sown, with sulfur, lime, or 
formalin. The fungicides mentioned have been used in the fol- 
lowing manner : sulfur and air-slaked lime in the drill at the rate 
of 100 pounds of sulfur and 50 pounds of lime, or a solution of 
formalin containing i pound of the latter to 30 gallons of water. 

Urocystis occulta (Wallr.) Reb. on rye {Sccalc ccrcalc), is an- 
other species of this genus of special economic importance in the 
eastern and north central states. 



CHAPTER XIV 

PROTOBASIDIOMYCETES 

I. RUST FUNGI 

Ured'males 

Arthur, J. C. Uredinales. North Amer. Flora 7 : 85-160. 1907. 
Arthur, J. C. Cultures of Uredineae; in 1899, Bot. Gaz. 1900; in 1900 and 

i90i,Journ. Myc. 8: 1902; in 1902, Bot. Gaz. 35: 1903; in 1904, Journ. 

Myc. 11: 1905; in 1905, Journ. Myc. 12: 1906. 
Blackman, V. H. On the Fertilization, Alternation of Generations, and 

General Cytology of the Uredineas. Ann. Bot. 18: 323-373. pis. 21-24. 

1904. 
Christman, a. H. Alternation of (fenerations and the Morphology of the 

Sporeforms in the Rusts. Bot. Gaz. 44: 81-101. pi. 7. 1907. 
Eriksson, J., und Henning, E. Die Getreideroste, ihre Geschichte u. Natur, 

sowie Massregeln gegen dieselben. 463 pp. 13 pis. 1896. Stockholm. 
Fischer, E. Die Uredineen der Schweiz. 590 pp. 342 figs. 1904. Bern. 
Klebahn, H. Die Wirtswechselden Rostpilze. 447 pp. 1894. (IiLxtensive 

bibliography, which see, especially for important papers by Klebahn and 

others.) 
McAlpixe, D. The Rusts of Australia. Dept. Agl. Victoria. 349 pp. 55 pis. 

1906. (Also extensive bibliography.) 
Olive, E. W. Sexual Cell Fusions and Vegetative Nuclear Divisions in the 

Rusts. Ann. Bot. 22: 331-360. pi. 22. 1908. 
Plowright, C. B. a Monograph of the Bridsh Uredineae and Ustilagineae, 

with an Account of their Biology, etc. 347 pp. 8 pis. 1889. 
Richards, H. M. On Some Points in the Development of yEcidia. Proc. 

Amer. Acad. Arts and Sci. 31 : 255-270. pi. i. 1895. 
SvDOW, P. Monographia Uredinearum. i. Puccinia. 972 pp. 1904. Leipzig. 

The Uredinales comprise about two thousand species, all of 
which are obligate parasites, and they represent perhaps the ex- 
treme of obligate parasitism. In no case has it been possible to 
grow these organisms upon artificial media or apart from the 
hosts beyond the stage of mere germination or of promycelial 
production. The host plants are predominantly the Spermatophyta, 
or seed plants, although a small number of these fungi are para- 
sitic upon ferns. The host deformities vary in external appear- 
ance from almost inconspicuous discolorations to hypertrophies of 
considerable size, on the one hand, or to extensive witches' brooms 

384 



PROTOBASIDIOMYCETES 385 

on the other. The production of spores, particularly the produc- 
tion of uredospores, is frequently in the nature of rust-like masses 
from which has been derived the common name applied to this 
family. Popularly the term rust has also been applied to certain 
leaf spot fungi, but this usage is ill advised. 

This order appears to be somewhat closely related to the smuts ; 
the presence of a promycelium (promycelial-like structure in the 
latter) giving, of course, the chief clue to this relationship. On 
the other hand, however, neglecting the feature of parasitism, 
there is a close relationship with the saprophytic Auriculariales, 
especially if we regard the teleutospore (promycelium, etc.) of the 
rusts as the all-essential spore form. 

The mycelium is generally local. In special cases, however, it 
may penetrate through a considerable extent of the host, and it is 
also occasionally perennial. It is almost invariably intercellular, 
abundantly branched, rather closely septate, and provided with 
haustoria. The effect of the mycelium upon the host is not to kill 
directly. In fact, the mycelium may develop within a tissue to an 
enormous extent, yet the cells of the invaded tissue may remain 
completely functional ; and death may result only when, after 
abundant fruiting of the fungus, the rupture of the epidermis is 
considerable, and doubtless the withdrawal of nutrients excessive. 
The spores which may be produced are of five general types, as 
given below. 

Spore forms, (i) Spermatia (or pycnospores), in spermogonia 
(or pycnidia) ; (2) aecidiospores, in cup-like organs, aecidia ; (3) 
uredospores, in pustules or sori ; (4) teleutospores, in sori simi- 
lar to the last ; (5) sporidia, upon a promycelium developed 
directly from the teleutospore. 

A species may include from one to five (all) of these types. 
The relations of these types one to another is definite and the 
number is ordinarily constant in the species. 

The spcnnatia are minute spores produced in flask-shaped 
conceptacles (spermogonia or pycnidia). They are supposed to be 
now generally functionless. Many mycologists assume that they 
had originally the function of one sexual gamete. The spermo- 
gonia are commonly associated more or less closely with the 
aecidia, although they may be associated with other spore types. 



386 FUNGOUS DISEASES OF PLANTS 

The cccidia are essentially cup-shaped bodies produced by the 
differentiation of a compact mass of hyphae growing perpendicular 
to the surface of the host. The outer layer of this body generally 
becomes a wall or peridium, the inner hyphae originating each, or 
each pair, a chain of one-celled spores separating at maturity. At 
first sterile cells alternate with the spore cells, but these practi- 
cally disappear by the time the spores are mature. Infection by 
the secidiospore commonly results in the production of uredo- 
spores, less frequently teleutospores, and in very few instances 
(so far as can be ascertained) another generation of secidiospores. 
The peridium is variable, and four types corresponding to four 
form genera may be recognized : in some cases a peridium is (i) 
absent (Caeoma) ; when present it is (2) toothed, the body being 
truly cup-shaped (^cidium), (3) fimbriate, the body being elongate 
(Roestelia), or (4) irregularly split and broken (Peridermium). 

The nrcdosporcs, produced ordinarily in masses or cushions 
(the sori), are hyaline, or generally yellow to dark brown, ovoidal 
or spheroidal spores borne generally upon pedicels, which are, 
however, usually deciduous. In a few genera the uredospores are 
produced in chains. The walls of these spores are frequently 
echinulate or warty, and there are from two to ten germ pores 
meridionally disposed. Germination may proceed immediately. 
The germ tube penetrates the host plant through the stomata, in 
general, and the uredosporic form may ordinarily produce re- 
peated generations of uredospores, under favorable conditions. 
Later in the season, or sometimes under less favorable conditions 
for propagative reproduction, teleutospores are developed. 

Teleutospores are ordinarily produced in sori more or less 
similar to the uredospores. The teleutospores are generally thick- 
walled resting spores, although in a few genera, or subdivisions 
of genera, they may germinate immediately. Germination con- 
sists in the production of a promycelium (basidium-like), which is 
generally divided into four cells, from each of which arises on a 
sterigma a small thin-walled spore, a sporidium (basidiospore). 

The sporidia germinate promptly under favorable conditions 
and may immediately penetrate the host. The mycelium de- 
veloped from this infection may give rise to aecidia and spermo- 
gonia, uredospores and teleutospores, teleutospores alone, etc. 



I'RU'roBASlDlOMYCErKS 2>^'j 

Heteroecism. In this order of fungi there has been developed 
not only great diversity in form and character of spores, and in the 
relationships of these t}'pes one to another, but also a very definite 
relationship between the different spore types and the host plants. 
Where more than a single spore type is present a species may 
either complete its entire life cycle upon a single host, that is, 
produce all spore forms in its life cycle on one host, or it may 
require two plants for complete development (in a few cases 
three) in regular order. The former group of rust fungi are 
termed aiittvcious and the latter hctcnvcions. Autoecism is the 
rule among fungi generally. Heteroecism is better developed in 
rusts than in any other group of living organisms, and it is with 
one or two exceptions confined to the rusts, so far as the fungi 
are concerned. There are more than 150 cases of heteroecism 
which have been experimentally demonstrated in this order, and 
this number will be greatly increased as the experimental work 
proceeds. Upon such hosts as the grasses, sedges, rushes (Gram- 
ineae, Cyperaceae, Juncaceae), and allied plants, the spore forms 
produced are quite generally the uredo and teleuto stages, or one 
or the other of these ; and in general, so far as the experimental 
work has been carried, such fungi have other stages, at least an 
aecidial stage, upon some dicotyledonous host. Indeed, in only 
one group of cases (the species of Puccinia on Phalaris) is the 
aecidial stage produced on another monocotyledonous host. Again, 
in no case of heteroecism has the ascidiospore been found to be 
capable of infecting also the host upon which it is borne. Since 
the teleutospore germinates by the development of a promycelium 
and sporidia, and in no other manner, it is precluded that the 
teleutospore may infect directly the host upon which it is pro- 
duced. The uredospores alone possess this capacity. 

In general, it would seem that the period of incubation may 
vary from eight to twenty days during the growing season, for 
most of the species of rusts. The time, however, will vary in the 
same species under different climatic conditions. 

The terminology of spore combinations. Based upon the asso- 
ciation of spore forms, that is, upon the number and kind of spores 
present in a particular species, Schroeter has proposed certain very 
convenient type names as below. First, however, it should be stated 



388 FUNGOUS DISEASES OF PLANTS 

that the spermogonial, aecidial, uredo, and teleuto stages are respec- 
tively represented by O, I, II, III, and it is here unnecessary to 
consider the fifth or sporidial stage ; the types, then, are as follows : 

^« forms with all stages; or O, I, II, III present. 

Brachy forms with aecidia omitted; or O, II, III present. 

Opsis forms with uredo omitted; or O, I, III present. 

Hoiii forms with spermogonia and aecidia omitted ; or II, III present. 

Micro forms with teleutospores only; or III present, germinating only 
after a resting period. 

Lepto forms with teleutospores only; or III present, germinating im- 
mediately. 

It is interesting to note that in the far North or in Alpine 
regions, as Fischer shows, the micro and lepto forms predominate. 
yEcidia occur alone in considerable number, and also hemi forms. 
Many hemi forms, particularly in such genera as Uromyces and 
Puccinia, have been insufHciently investigated, and will doubtless 
prove to be eii forms, mostly hetercecious, that is, eii-hctero forms. 

No terms applicable alike to all genera having similar spore 
forms, based upon some common root and the prefixes above 
mentioned, expressing also heteroecism and autoecism, have been 
suggested. It seems desirable for many reasons to employ as this 
root the word Jtredo, and since it will be used in combination with 
these prefixes, there can scarcely be any confusion, although uredo 
is a form-genus name. With this nomenclature a form which is 
eu-heteroecious will be termed cnJietcronrcdo, and the other combi- 
nations will be made in an analogous manner. 



II. FAMILIES AND GENERA 

According to Fischer the order may be most conveniently sub- 
divided into four families, and the characters employed as a basis 
of this system of classification are for the most part those of the 
teleutospores. 1 

1 Arthur has proposed for the Uredinales an entirely new system of classifica- 
tion (Resultats scientifiques du Congres International de Botanique, Vienne, 1905, 
pp. 331-348). By this system many more genera would be constituted since, in 
addition to the usual characters, the completeness of the life cycle with respect 
to the four main stages is made generically diagnostic. He has also introduced 
the iermspvcnium, (Eciiim, uredinium, and teliiim in substitution for teleuto, uredo, 
aecidial, and spermogonial stages. 



PROTOBASIDIOMYCETES 389 

1. Pucciniaceae. The teleutospores usually consist of a single 
cell or a vertical row, sometimes, however, united into the form of 
a relatively small head. The spores are borne on a simple or com- 
pound pedicel. The uredospores are single, on hyaline, deciduous 
pedicels. The aecidia are generally provided with a well-developed 
peridium. The genera here considered are Uromyces, Puccinia, 
Gymnosporangium, Gymnoconia, Phragmidium. 

2. Cronartiaceae. The teleutospores are without pedicels, and 
they originate in chains, or series, more or less free at maturity, or 
united into complex bodies. Chrysomyxa and Cronartium are the 
important genera. 

3. Coleosporiaceae. The teleutospores are united into a layer 
generally wax-like in texture, and orange-red in color. The spores 
are generally without pedicels, at first unicellular, but soon dividing 
into four cells, that is, to form the promycelium within the spore, 
each cell of which, therefore, produces a sterigma and basidiospore. 
The genus Coleosporium includes the more important species. 

4. Melampsoraceae. The teleutospores form a closely adherent 
crust-like layer, each cell of which germinates by a typical promy- 
celium. The uredospores are borne singly, and the aecidia are with 
or without peridia. Melampsora is the chief genus. 

The genera above mentioned may be briefly described as follows : 

Uromyces. The teleutospores are unicellular with a terminal 
germ pore ; the uredospores are generally provided with many evi- 
dent germ pores ; the aecidia are provided with peridia, the aecidio- 
spores are without germ pores, and the spermogonia are spherical 
with minute circular ostiola. 

Puccinia. This genus is similar to Uromyces except that the 
teleutospores are two celled. Unicellular teleutospores may also 
occur in some species. 

Gymnosporangium. The teleutospores are commonly two celled, 
exceptionally three or four in a row. They are borne in pustules ; 
and, at maturity, owing to the development of substances resulting 
partially from the gelatinization of the long pedicels, they are 
pushed out into jelly-like masses, sometimes horn-like in form. 
The spores are often provided with several germ pores arising 
near the side wall, though apical germ pores may be present. 
There are no uredospores, and the aecidia (roestelia) are often 



390 FUNGOUS DISEASES OF PLANTS 

jug-shaped or cylindrical, with thick-walled peridia. The aecidio- 
spores are highly colored, and possess numerous germ pores. 
They arc invariably accompanied by flask-shaped spermogonia. 

Gymnoconia. This genus resembles Puccinia in the general 
characters of the teleutospore, and no uredospores are present. 
The most abundant spore form is that of the caeoma stage. The 
latter is an ascidium without a peridium, the spores being borne in 
chains ; and in this case the spores are generally highly colored, 
orange to orange -yellow. The spermogonia are numerous, spherical, 
and very simple in form. 

Phragmidium. The teleutospores are made up of three or more 
cells in a row borne upon a persistent pedicel. Uredospores are 
present, and these are borne in pustules bordered by paraphyses ; 
each spore possesses several germ pores. The ascidia are also of 
the caeoma type, but here there is an outer border of unicellular, 
curved paraphyses. The spermogonia are flat or discoidal. Species 
of this genus occur only upon Rosaceae. 

Chrysomyxa forms a teleutosporic cushion, the cells of which 
are closely adherent. These spores germinate immediately by the 
production of a promycelium. The uredospores are borne in chains, 
as are also the aecidiospores, the two kinds being more or less 
similar. The aecidia, however, are provided with well-developed 
peridia. 

Cronartium is characterized by teleutospores united into a cylin- 
drical column, each spore germinating immediately by the pro- 
duction of a promycelium from near the apex. The uredospores 
are borne singly on pedicels within a semispherical body possess- 
ing a differentiated peridium. This latter structure is provided with 
a small terminal pore or mouth. 

Coleosporium. In this genus the teleutospores are closely 
adherent, with a rounded, thickened, gelatinizing apex. The 
sterigmata are long, and the sporidia large, ovate, and flattened. 
The spore, at first a single cell, divides to produce a series of four 
inner promycelial cells. 

Melampsora. The teleutospores are generally unicellular and 
closely united into indefinite crusts. The uredospores are borne 
singly, often interspersed with paraphyses. The aecidia are of the 
casoma type, and paraphyses are occasionally present. 



PROTOBASIDIOMYCETES 



391 



III. SYNOPSIS OF SPECIES 



Arranging the species here discussed, together with a few others 
as examples, in groups according to the spore forms and heterce- 
cism or autoecism, we have the following : 



Euautouredo (Stages O, I, II, III) 



Hosts 



Lev. 



Uroiiiyces Trifolii (Hedw.) Ldv. . 



Uroiiiyccs appendiculatus (Pers.; Phaseolus vulgaris (beans) (also species 

of Dolichos and Lablab.) 
Trifolium hybridum, T. incarnatum, T. 
pratense, T. repens, etc. (various 
clovers) 
Beta vulgaris (wild and cultivated beet) 
Asparagus officinalis (asparagus), etc. 
Helianthus annuus (sunflower), etc. 
Viola spp. (violets) 
Certain Labiatae (mints) 



Uroniyces Betcr (Pers.) Tul. . 
Puccinia Asparagi De C. . 
Puccinia Heliaiithi Schw. 
Puccinia Violce (Schum.) De C 
Puccinia Metith^ Pers. 
Gymnoconia Peckiana (Howe) 

Tranz Rubus occidentalis (blackberry), etc. 

PJi rag ni idi ti in s u l> c or/ it i 11 ni 

(Schrank) Wint Rosa spp. (various roses) 



Euheterouredo (Stages O, I, II, III) 

O, I 



Hosts 



II, III 



Uromyces Pisi (Pers.) 
De Bary. 



Euphorbia Cyparissias Pisum sativum (pea) 

Lathyrus pratensis, 



Puccinia graminis Pers. Berberis vulgaris 

(barberry) 
Berberis Lycium 



etc. 
Avcna sativa (oats) 



Berberis Aquifolium 



Hordeum vulgare 

(barley) 
Secale cereale (rye) 
Triticum vulgare 
(wheat) 
Puccinia Sorghi Schw. Oxalis cymosa (oxalis) Zea mays (Indian corn) 
Puccinia Phleipratcnsis Phleum pratense 

Eriks. & Henn. (timothy), etc. 

Puccinia ru bigo-i'c ra Boraginaceas Triticum spp., Avena 

De C. sativa, etc. 

Puccinia Pruni-spinosce Hepatica acutiloba Prunus spp. (plum, 

Pers. (hepatica) peach) 



FUNGOUS DISEASES OF PLANTS 



C/nysoi/iyxa Rhododendri Picea excelsa 

(DeC.) De Bary (Norway spruce) 

Croiiartiitin Ribicola Pinus strobus (white 

Fisch. de Waldh. pine) 

Coleospon'iim Seiiecionis Pinus sylvestris 

Pcrs. (Scotcii pine) 

Mcldiiipsofa //rinii/cFTuX. Pinus sylvestris 

(Scotch pine) 



Rhododendron ferrugi- 

neum 
R. hirsutum 
Ribes spp. (currant, 

gooseberry) 
Senecio vulgaris 
S. sylvaticus 
S. viscosus, etc. 
Populus tremula 

(poplar) 



Opsiautouredo (Stages O, I, III) 

Hosts 
Piiccinia Tragopogi Pers Tragopogon spp. (salsify) 



Opsiheterouredo (Stages O, I, III) 



Hosts 



O, I 



Gymnosporangiuni ma- Pyrus Malus (apple) 
cropHs Lk. 

Pyrus coronaria (wild 
crab) 
Gyinnosporaiigiuiii globo- Pyrus Malus (apple) 
Slim Farl. 

Pyrus communis 

(pear) 
Pyrus americana 
Cydonia vulgaris 
(quince) 
Gymnosporangiiim Sabi- Pyrus communis 

nee (Dicks.) Wint. (pear) 

Gytnnosporatigium clava- Crataegus tomentosa 
ricrforme (J acq.) Rees 



III 

uniperus virginiana 

(red cedar) 
. virginiana (red cedar) 

. virginiana (red cedar) 

. virginiana (red cedar) 

. virginiana (red cedar) 
. virginiana (red cedar) 

. Sabina 

. communis (common 
Juniper) 



Brachyautouredo (Stages O, II, HI) 

Piicciiiia Hicracii (Schum.) Mart. . 
Piiccinia siiaveolens (Pers.) Rostr. . 



Hosts 
Hieracium spp. 
Cirsium arvense (Canada thistle) 



Hemiuredo (Stages II, HI) 

Hosts 
Uromyces CaryopJiylliniis (Schrank) 

Wint Dianthus Caryophyllus (carnation), etc. 

Uromyces scutcllatns (Schr.) Wint. Euphorbia spp. (spurges) 



l'R( )T()RASII)I( )M VCETRS 393 

Uromyces Rumicis (Schum.) Wint. Rumex spp. (sorrels) 

Hemileia vastatiix Berk. & Br. . . Coffea arabica (coffee) 

Puccinia Chrysanthemi Roze. . . Chrysanthemum spp. 

Puccinia Polygoni Pers Polygonum spp. 

Pmcinia Allii De C Allium Cepa (onion) 

Microuredo (Stage III) 

Uro»iycesSoIida<j;iiiis(':r>oxnxn)W\&'s,^\. Solidago spp. (goldenrod) 

Puccinia Ribis De C Ribes spp. (currant, gooseberry) 

Puccinia fusca Relhan Anemone nemorosa, etc. 

Leptouredo (Stage III) 

Puccinia nia/i'accarum Mont. . . Althaea rosea (hollyhock), etc. 
Puccinia Xanthii Schw Xanthium spp. (cocklebur) 

(Stages O, III) 
Uromyces teppcrianus Sacc. . . . Acacia spp. 

(Stages O, I) 

yEcidiuin elatinunt Alb. & Schw. . Abies spp. (firs) 

yEcidimn Grossularicp Schum. . Ribes spp. (currant, gooseberry) 

Periderniiuni Engelniannii Thum. Pinus Engelmannii 

(Stage II) 

Uredo Fici Cact Ficus carica (fig) 

Uredo Gossypii Sager Gossypium hirsutum (cotton), etc. 

During the past few years considerable activity has been mani- 
fest in the study of the cytology and possible fertilization processes 
in the Uredinales. It had been known since the studies of Sappin- 
Trouffy and Dangeard that the binucleate condition of the teleuto- 
spore and of the mycelium preceding it leads finally to a fusion of 
these two nuclei preceding the development of the promycelium. 
The recent studies have been directed primarily toward a knowl- 
edge of the origin of this binucleate condition. Blackman in some 
extensive studies of a caeoma stage, in particular, demonstrated what 
he believed to be a fusion phenomenon in the following manner : 
During the early development of this stage numerous gametic 
branches arise. These come in contact in pairs, the older and 



394 



raiNGOUS DISEASES OF PLANTS 



larger branch cutting off an apical cell. The smaller gamete in 
time loses its nucleus by migration through a pore into the larger 
gamete, and the cells thus provided with two nuclei become each 
properly the basal cell of one of the chains of spores which arise 
in this type, corresponding to the aecidium, each spore of which 




Fig. 194. PiiKAGMiDiuM sPEciosuM : Df-velopment of /Ecidiospores 
(After Christman) 

(7, progametes ; b, gamete and sterile cell ; c, after gametic fusion and nuclear 
division ; d and c, spore production 

possesses paired nuclei. He would also homologize the apical cell 
of the larger gamete with the trichogyne of certain lower plants, and 
would assume that in the phylogeny of these plants the spermatia 
were functionally in connection with this Organ. The work of 
Christman and Olive on this and other rust fungi in part confirm 
Blackman's results. They are also able to identify the gametes, but 
the communication between these two adjacent cells is generally, 



PROTOBASIDIOMYCETES 395 

however, effected by a dissolution of the upper portion of the cell 
walls in contact, thus securing a union of two cells. From these 
united cells, with two' nuclei, as a basal structure arise the chain of 
spores as before. The evidence offered seems to thoroughly explain 
the origin of the binucleate condition. While there are many 
exceptions which might be noted, there is in general, in the case 
of a species showing all spore types, the following nuclear life 
history. The mycelium which produces the spermogonia and the 
secidium is uninucleate. There is a fusion of cells in the ascidium 
(where such organ is present) and the ascidiospores are binucleate. 
The mycelium which produces the uredospores and the teleuto- 
spores is binucleate, and these spores are themselves binucleate 
(in this type). Fusion of the nuclei results at about the time of ger- 
mination of the teleutospore, so that the sporidia are uninucleate. 
It is, however, unnecessary here to enter into a more detailed dis- 
cussion of these phenomena. 

IV. CLOVER RU.ST 

Unmiyces Tnfolii (Hedw.) Lev. 

Howell, J. K. The Clover Rust. Cornell Agl. Exp. .Sta. Built. 24: 129- 

139. 1890. 
Pammel, L. H. Clover Rust. Iowa Agl. Exp. Sta. Built. 13: 51-55. 1891. 

Habitat relations. The clover mst is ordinarily a common 
disease of various species of Trifolium. It causes a disease of the 
clovers more serious in many instances than that produced by 
Pseudopeziza, already mentioned. The Uromyces is cosmopolitan, 
and the more susceptible hosts are important forage plants. Among 
the clovers the following species are frequently infested : red clover 
(Trifolhint pratensc), hybrid clover {Trifolium Jiybridtini), white 
clover {Trifolium rcpcns), and crimson clover {Trifolium iucar- 
7iatum). The prevalence of the disease apparently varies greatly 
with the season, and is to a considerable extent determined by the 
spring conditions. We have, however, no very accurate knowledge 
of the climatic relations of this fungus. 

This fungus is taken as a type of an autoecious member of the 
genus, as it may have all stages on the same host plant. The 
various stages commonly occur upon Trifolium repeus and also 



396 



FUNGOUS DISEASES OF PLANTS 



upon Tvifolium, caroliiiianmn, much less frequently, however, upon 
some of the other species mentioned. In general, the spermogonial 
and aecidial stages are not commonly found upon the red clover, 
the host upon which the other stages are perhaps most frequent. 

Nevertheless, the reported 
absence of aecidial stages 
upon this host in certain 
regions may be due to the 
fact that careful examina- 
tions have not been made 
at the proper season. 

The fungus. The my- 
celium corresponds very 
closely to that described 
as generally characteristic 
of the whole order. It is 
considered to be local. 
The spermogonia and 
aecidia generally appear 
during very early spring 
or at almost any time dur- 
ing open winter. They 
occur upon the under sur- 
faces of the leaves and on 
the petioles. The secidio- 
spores {14-23/X in diam- 
eter) germinate readily in 
water, and under favor- 
able conditions infection 
in the greenhouse or in 
the open may be secured, 
with the production of uredosori within two weeks. The uredo- 
spores, as shown in Fig. 195, d, measure about 22—26 x 18— 20/x. 
These spores also germinate readily, and repeated crops of the 
uredospores may be produced, possibly in some cases extending 
into the winter, and even carrying the fungus through the year. 
Teleutospores are produced, however, and these may occur in 
sori with uredospores, or in independent sori, as the season 




Uromyces Trii-oi.h : Clovkk Rust 



PR( ) r( )BAS1I)1()MVCETES 



397 



advances. These spores are 20-35 X 15-22/u., and a spore ger- 
minates by the production of the characteristic promyceHum, di- 
vided ordinarily into four cells, each producing its sporidium. The 
germination of the teleutospore would seem to take place ordinarily 
several weeks prior to the appearance of the spermogonium and 
aecidium, both of which arise only from teleutosporic infection. 
The failure of the spermogonia and ascidia on red clover, pre- 
viousl)' referred to, may also indicate that the teleutosporic form 
does not so readil)- infect this species of host. 




Fig. 196. I'jfo.ui-cjzs apphxdiculatus : Rust of Beans. (Photograph by 
H. H. Whetzel) 

As a rule, control measures seem to be unnecessary ; at any rate 
no practical preventive methods are known. 



V. RUST OF BEANS 

Urotnyces appetidiculatus (Pars.) Lev. 

De Barv, a. Recherches sur le d^veloppement de quelques champignons 

parasites. Ann. d. Sci. nat. Bot. (Ser. 4) 20: 68-99. i^^S- 
Whetzel, H. H. Bean Rust. Cornell Agl. Exp. Sta. Built. 239 : 298-299. 
figs. 113-115. 1906. 

This fungus is widely distributed, occurring on the bean {Phaseo- 
his vulgaris) and other related species. It is also reported in south- 
ern latitudes on relatives of the cowpea, such as DoHchos ornatiis, 



398 FUNGOUS DISEASES OF PLANTS 

Lablab vulgaris, Vigna marginata, etc. The fungus commonly 
appears late in the season, and it is often destructive to foliage, 
causing early maturity and lessened production of the beans. There 
is great difference in susceptibility of varieties both among dwarf 
and pole sorts. Moreover, the fungus is harbored by the old leaves 
and vines. Burning these would reduce the quantity another year. 
The effect of turning under affected parts does not seem to have 
been tested. Selection of resistant varieties would seem to be 
possible for each locality. The spermogonia and aecidia are very 
light in color. The secidiospores are colorless and polyhedral, 
17-32 X 14-23 /a; the obovate, minutely echinulate uredospores, 
which are 24-33 X 16-20 /a, occur in rather minute sori ; and the 
teleutospores are broadly elliptical, measuring 26-35 X 20-26 /i, 
and each spore is provided with a large, terminal papilla. 

VI. RUST OF VETCH AND GARDEN PEA 

Uromyces Fist (Pers.) De Bary 

De Bary, A. Recherches sur le ddveloppement de quelques champignons 

parasites. Ann. d. Sci. nat. Bot. (Ser. 4) 20: 68-99. 1863. 
Klebahn, H. Die wirtswechselden Rostpilze, I.e., p. 330. 

In the United States this species is not so prevalent as the pre- 
ceding species. It shows, however, an interesting heteroecism. The 
pycnidia and aecidia occur on Euphoj-bia Cyparissias, while the 
uredospores and teleutospores are found upon LatJiyms pratcnsis, 
Vicia cracca, Pisnni sativiiui, and Pisuin arvensc. In addition, a 
number of other hosts have been given for stages II and III. In 
this rust the aecidia and spermogonia are together irregularly dis- 
tributed on the under surfaces of the leaves. The aecidia are 
numerous, with deeply cleft peridia, the cells of which have a very 
slight lumen. The aecidiospores are more or less isodiametric, and 
from 18 to 22 /x in diameter. The spore wall is decorated with fine 
wart-like projections. The uredosori are small, pulverulent, and 
distributed over the leaf. The uredospores are more or less spher- 
ical, and measure 21-25 /"■• The wall is thick and the 4-5 germ 
pores are evident. The teleutospores are obovate, with short, hya- 
line stalks. The wall is uniformly thickened and beset with fine 
warts, except at the apex, where there is a conspicuous, flat papilla. 



PROTOBASIDIOMYCETES 399 

VII. BEET RUST 
Uromyces Betce (Pers.) Tul. 

KiJHN, J. Der Rost der Runkelriibenblatter, Uromyces Betce. Bot. Zeitg. 27 : 

540-544. 1869. 
McAlpine, D. The Rusts of Australia, /. r., Uromyces betce (Pers). Kiihn., 

loo-ioi. pi. 1 7, Jigs. I48-I4g ; pi. 43, fig. 316 ; pi. H. 

The spermogonia occur in small, yellowish groups, and the ascidia 
in similarly colored but somewhat larger spots, within which they 
may be arranged in circular or regular form. The aecidia are 
saucer-shaped and white, the aecidiospores more or less isodiametric, 
1 7-36 /i in diameter, with orange-colored contents. Both the uredo 
and the teleuto stages occur in sori irregularly distributed over the 
surfaces of the leaf, often circularly disposed. The uredospores are 
mostly obovate, 2 1 -24 X 3 5 /u.. The walls are provided with some- 
what distant echinulations and two opposite germ pores. The 
teleutospores are similarly obovate, 18-24 X 25-32^1. The wall is 
scarcely thicker at the apex, with an apical germ pore, and a veiy 
distinct papilla of the same diameter as the germ pore. The 
pedicel is short and persistent. This fungus is prevalent in 
Australia, and it is not uncommon in Europe ; but in the United 
States it appears only to have been observed in California. This 
species is found on cultivated beets {Beta vtilgaris), also on wild 
species of this genus. According to the observations of Kiihn the 
mycelium may be biennial in the host, forming aecidia practically 
throughout the year. 

VIII. CARNATION RU.ST 

Uromyces CarxophylUiuis (Schrank) Wint. 

Atkinson, George F. Carnation Diseases. Amer. Florist 8 : 720-728. figs. 

1-33- 1893- 
Stewart, F. C. Combating Carnation Rust. N. Y. (Geneva) Agl. Exp. Sta. 

Rept. 15: 461-495. 1895. (Also Built. 100.) 
Stuart, Wm. Some Studies upon Carnation Rust. Vermont Agl. Exp. Sta. 

Rept. 8 : 1 15-1 18. 1894. 

Occurrence and effects. The fungus causing carnation rust was 
recognized in Europe more than a century ago, and it was properly 
named during the first half of the nineteenth century. It has long 
been recognized as a common disease of the carnation {Dianthiis 



■400 



FUNGOUS DISEASES OF PLANTS 



CaryopJiylbis), and it occurs also upon other species of this genus, 
and upon some other related genera. Prior to 1890 it had not been 
noted in the United States, and it is doubtful if it was previously 
common. Since that time, however, it has rapidly spread through- 
out the regions where carnations are grown either under glass or 
in the open. For a few years after its abundant appearance in this 
country it threatened to cause a panic in carnation growing, and 
florists' magazines and papers devoted much space to a discussion 
of the disease, methods of control, susceptibility of varieties, etc. 




Fig. 197. Carnation Rust 



It is now permanently established as one of the regularly antici- 
pated diseases of the carnation, but there is no fear that its pres- 
ence in any way jeopardizes carnation growing as an industry, at 
least so far as the best growers are concerned. 

Host resistance. Since the appearance of this pest there has 
been opportunity for selection, so that resistant varieties might 
be secured, or at least so that the more susceptible sorts might 
be discarded, particularly when more or less similar varieties 
may be grown which are less sensitive. Perhaps no commercial 
variety of this plant has proved more susceptible to the rust than 
the Scott. The susceptibility of this variety seemed to be intensi- 
fied the longer it was in the trade. The Jubilee (scarlet) and 
Flora Hill (white) have also proved susceptible, and these have 



PROTO BA S 1 1) I O M YC ET ES 



401 



been to a very considerable extent discarded by growers who can- 
not handle the plant so as to prevent rust. On the other hand, 
varieties like the Enchantress (daybreak pink) and Lawson (pink) 
have under a variety of conditions demonstrated a high degree of 
resistance. Nevertheless, the conditions under which the plants 
are grown affects to a considerable extent the amount of the rust. 
Of two growers using cuttings from the same stock with different 
regard for sanitation and different methods of cultivation, the one 
may find the rust abundant in his houses, and the other may be 
able to grow plants practically free from it. It is certain that poor 
ventilation and conditions permitting the deposit or retention of 
drops of water upon the surfaces of the leaves is more conducive 
to the spread of the fungus, but its approximate relations to 
environmental factors have not been determined. 

The fungus. The life history of this fungus is incompletely 
known. The uredosporic stage is the common method of propaga- 
tion, but the teleutosporic stage may also be found under the condi- 
tions of greenhouse or garden. The uredospores are more or less 
spherical or ellipsoidal in form, ordinarily varying from 24-35x21- 
261JL. The cell wall is thick and sparsely beset with minute spines. 
The uredosporic pustules are pulverulent, light chestnut brown in 
color, and may be found upon leaves or stems. The teleutospores 
are not dissimilar in form to the uredospores, and are commonly 
ellipsoidal, varying from 20-35 x 18-25 /x. The rather uniformly 
thickened chestnut brown membrane is marked by minute wart- 
like markings best seen in the dry condition. The spores possess 
terminal germ pores marked by a papillate, hyaline covering. The 
pedicels are short and colorless. The uredospores germinate read- 
ily in water, and the experiments made by Stewart indicate that 
they are unusually resistant to many fungicides and toxic agents. 
A solution of 1-500 copper sulfate was required to give inhibition 
of germination, and a still stronger solution to entirely prevent 
germination. On the other hand, potassium sulfide i-iooo pre- 
vented germination, and even weaker solutions inhibited consider- 
ably this process. 

It would appear that the mycelium is not greatly localized 
in the host, but no accurate determination of this point can be 
cited. Furthermore, few inoculation experiments have been made 



402 FUNGOUS DISEASES OF PLANTS 

in order to determine the possibility of spreading the disease 
to vigorous adult plants. Observation would indicate that adult 
plants may be affected, and consequently that the disease may be 
spread rapidly during the growing season. In fact, it is only upon 
this basis that the rapid spread of the fungus can be accounted 
for. Yet there is very little experimental data upon which to rely 
for confirmation of this statement. 

Control. Three methods of control have been considered and, 
when necessary, practiced, and these in addition to a maintenance 
of the best general conditions of the environment with respect to 
sanitation. In the first place, resistant varieties should be grown 
as far as possible. Secondly, it is desirable, where the rust 
abounds, or where rust-susceptible varieties must be grown, to 
have simple V-shaped wire mesh supports placed between the rows 
in order to hold the foliage away from the moist soil, and also to 
permit of watering without constant wetting of the leaf surfaces. 
Thirdly, it may be necessary to employ fungicides when other 
methods fail. In such cases the plants may be sprayed once each 
week with a solution of copper sulfate about 1—500 (i lb, copper 
sulfate to 12-15 gallons of water), or with a solution of potassium 
sulfide I ounce to i gallon, 

IX. UROMYCES: OTHER SPECIES 

Uromyces scutellatus (Schr.) Wint. apparently occurs as a very 
common parasite of a large number of species of Euphorbia. The 
species is ordinarily broken up into different forms, which vary very 
slightly one from another in general appearance and considerably 
in extreme size, the uredospores being 17-35 X 14-2 3 /*, and the 
teleutospores 20-38 x 16-25 /u,. Whether this fungus is, in any of 
its forms, a euheterouredo, or invariably a hemiuredo, as it appears 
to be, is not definitely determined. 

Uromyces Rutnicis (Schum) Wint. This species is found on 
many members of the genus Rumex. It appears to be a 
hemiuredo. 

Uromyces Solidaginis (Somm.) Niessl, This is commonly con- 
sidered to be a microuredo and occurs upon several species of 
Solidago. 



PROTOBASIDIOMYCETES 



403 



X. ASPARAGUS RUST 
rued Ilia Aspanrgi Dc C. 

Halsted, B. D. The Asparagus Rust; Its Treatment and Natural Enemies. 

N. J. Agl. Exp. Sta. Bulk. 129: 1-20. pi. 1-2. 1898. 
Halsted, B. D. Experiments with Asparagus Rust. N. J. Agl. Exp. Sta. 

Rept. 11: 343-347- 1898. 
SiRRiNE, F. A. Spraying for Asparagus Rust. N. Y. Agl. Exp. Sta. Built. 

188: 122-166. 1900. 
Smith, Ralph E. The Water-Relation of Puccinia Asparagi. liot. Gaz. 38 : 

19-43. Jigs. I -2 1. 1904. 
Smith, Ralph E. Further Experience in Asparagus Rust Control. Calif. Agl. 

Exp. Sta. Built. 172 : 1-22. 1906. 
Smith, Ralph E. Asparagus and Asparagus Rust in California. Calif. Agl. 

Exp. Sta. Built. 165: 1-95. Jigs. 1-4^. 1905. 
Stone, G. E., and Smith, R. E. The Asparagus Rust in Massachusetts. Mass. 

(Hatch) Agl. E.xp. Sta. Built. 61 : 1-20. 1899. 

Distribution and general 
effects. The fungiis caus- 
ing asparagus rust was de- 
scribed a century ago, and 
the effects of this fungus 
upon the asparagus plant 
have been known perhaps 
almost as long by growers 
in Europe. It has been, 
however, in general of 
no great consequence as 
an asparagus disease; but 
upon making its appear- 
ance in America, some- 
what more than twelve 
years ago, this rust began, 
under our conditions, im- 
mediately to assume an 
unexpected importance. 
In a brief space of time 
the asparagus-growing 
interests of the countiy were seriously threatened. According 
to Halsted, who followed closely its early spread in this country, 
it became in 1896 a serious pest in New Jersey, Delaware, 




Fig. 19S. Puccinia Asparagi : Rust of 
Asparagus 



404 FUNGOUS DISEASES OF PLANTS 

Long Island, and parts of New England, In succeeding years 
it became more serious in those sections, and spread also rapidly 
southward and westward. It has, however, varied greatly in 
destructiveness in the eastern states from year to year, but on 
the whole the asparagus industry suffered such a check that a 
much more complete study has been made of methods of culture, 
of direct means of control, and of varietal resistance. As a result, 
in the East the asparagus interests have been gradually adapted to 
the new conditions, and it is not likely that the former epidemics 
have left any very serious impression upon this product as grown 
for immediate marketing. 

In 1 90 1 the rust seems to have been of the first serious conse- 
quence in southern California, spreading northward, and doing the 
greatest damage up to about 1905, since which time the energetic 
control measures suggested by Smith have been effective with the 
best growers in many localities. 

Climatological relations. It has been demonstrated that the 
prevalence of asparagus rust in most localities bears a very definite 
relation to climatological and other conditions. When the air re- 
mains dry throughout the summer, rust is very largely prevented. 
Occasional rains with intervening periods of low humidity do not 
constitute favorable conditions for the fungus. A heavy formation 
of dew is almost inevitably requisite to the abundance and spread 
of the disease. This latter is of much practical importance in Cali- 
fornia, and referring to the conditions in that state, Smith says, 
^'The amoimt of rust varies directly and exactly zvit/i the amount of 
dew, and so long as there is little or no dezv, there can be no rust." 

Again, on light soil which has a tendency to dry out during 
the growing season, rust is prevailingly worse than on land 
where the plant secures the amount of moisture needed by the 
roots. The greater susceptibility on such lands has been attributed 
to the reduced vigor of the host plant, but here also a dew relation 
may often be a possible factor. Nevertheless, good cultivation is 
favorable to the host plant, as innumerable experiments have 
demonstrated. It should further be noted that the asparagus 
under half shade is commonly free from rust. 

Host plants. Among the varieties of asparagus commonly grown 
in the United States, the Palmetto has proved most resistant, this 



PROTOBASIDIOMYCETES 



405 



resistance being particularly noticeable when the varieties are grown 
side by side for a period of years. The final effect of the rust 
upon the plant from year to year is a determining factor in adapt- 
ability. Sirrine was unable to confirm the observations as to the 
high resistance of the Palmetto as grown on Long Island, but 
it is suggested that a weaker strain is there in use. Conover's 
Colossal and the various forms related to this, or the selections 
from it, are types of the more susceptible sorts. These, moreover, 
are the varieties upon which the 
canning industry depends. The 
fungus also occurs on some wild 
species of asparagus such as As- 
paragjis capsicjts and Aspai-agus 
niantimns. 

The spore forms. No impor- 
tant distortions are made upon 
the host by different stages of 
this fungus. All spore forms 
are produced on stems and 
twigs (Fig. 198), and the uredo 
and teleuto stages occur also 
on the leaf-like branches. The 
aecidial stage may appear at 
almost any point in the United 

States with a growing season no shorter than that of northern 
New Jersey. The secidia appear in rather long, light green, 
cushion-like areas. They are short-cylindrical, with a white perid- 
ium, and the spores appear orange colored from the contents ; 
the wall, however, is hyaline and granulose. The spores meas- 
ure I 5-1 8 /A in diameter. They may germinate immediately, and 
when dry, some at least retain the capacity for germination 
throughout several weeks. Penetration of the host plant is ap- 
parently through the stomata. The spermogonia appear in small 
yellow clusters. 

The uredo or red rust stage appears in early summer, or shortly 
after the secidial stage, at first in scattered, deep brown sori, but 
afterwards the latter may be confluent. The uredospores are yel- 
lowish brown, with thick walls, fine yellow markings, and provided 




Y\G. 199. PUCCINIA AsPARAGi: 

Teleutosporic Sorus 



4o6 FUNGOUS DISEASES OF PLANTS 

with four germ pores. They measure 21-24/x. They are produced 
in such abundance as to be dusted in quantity upon any passing 
object or taken in clouds by the wind for some distance. They 
are unquestionably the chief means of distributing the disease 
during the growing season. It has been found (Smith) that their 
vitality upon drying is not retained for more than a few months. 

The black rust stage appears later in the season, apparently as 
the conditions for uredosporic formation become unfavorable. The 
sori are black-brown, and while for a time protected by the epi- 
dermis, they are finally exposed. The teleutospores are elliptical, 
slightly constricted, as a rule, and measure 30-60 x 21-28 /i. The 
wall is thick at the apex, and the pedicels very long. These spores 
show a more or less persistent attachment to the host. Unicellular 
teleutospores also occur. They have been germinated towards the 
middle or end of winter, with the characteristic promycelium and 
sporidia. It is believed that the general infection in cultivated 
fields each season results from aecidiospores produced on wild or 
escaped plants, and not directly from the germination of teleuto- 
spores which have remained in or about the soil. 

Control. The numerous attempts which have been made to 
control the asparagus rust by means of Bordeaux mixture have 
been more or less unsuccessful. Nevertheless, Sirrine, in experi- 
ments on Long Island, and later others have used to advantage 
a Bordeaux prepared with resin. The mixture which may be 
recommended is as follows : 

Bordeaux mixture, 5-5-40 formula, 40 gals. 
Resin mixture, 2 gals., diluted to 10 gals. 

The resin preparation consists of resin, 5 lbs. ; potash lye, i lb. ; fish oil, i pt. ; 
and water, 5 gals. 

In California it has been found that under certain climatic con- 
ditions thorough spraying with sulfur, either as dust or liquid, is 
an efficient preventive, the prevention resulting from the fumes. 
In any case, however, where control consists in the use of sprays, 
provision should be made for the best circulation of air possible, 
that is, the field should be as free from obstructions around the 
border, and the rows should be a sufficient distance apart so as 
not to make the conditions any more favorable than possible for 
high moisture content of the air. Thorough cultivation should be 



PROTOBASIDIOMYCETES 407 

given, and requisite irrigation is desirable when there is a tend- 
ency for drying out to affect the health of the plant during the 
summer. It would appear, however, that the best method of con- 
trolling the fungus is by the selection of resistant sorts. Since the 
Palmetto variety has shown itself fairly resistant in the East, it is 
probable that other sorts may be obtained which will possess some 
of the desirable qualities of the Conover, with the resistance of 
the Palmetto. So far as I am aware, no extensive report has 
been made upon the resistance of European varieties under our 
conditions. 

XL VIOLET RUST 
Piiccinia Violce (Schum.) De C. 

Arthur, J. C, and Holwav, E. W. D. Violet Rusts of North America. 
Minn. Bot. Studies Built. (Ser.) 2: 631-641. 1901. 

This species of violet rust is parasitic on about sixty different 
hosts in the genus Viola throughout North America and parts of 
South America, also Europe and Asia. The spermogonia and 
aecidia occur early in the season in light brown spots scattered 
over leaves and stalks. The ascidiospores are ovoidal, 16-24 X 
10-18/X. The uredospores and teleutospores follow in succession, 
both of these on the under surfaces of the leaves, producing no 
definite spots ; yet a large number of sori may become confluent 
so as to present the appearance of dark brown areas. The fungus 
is not of much consequence from an economic point of view in 
relation to violet culture, but it is, nevertheless, the most common 
of the five (assuming the validity of some species) violet rusts. 

XIL MINT RUST 

Fuccinia Alenthce Pers. 

This is a species apparently well distributed throughout a large 
part of the world on about thirty-five members of the mint family. 
The fungus is closely related to a number of other species whose 
host plants are also certain mints. In fact, more than thirty species 
of rusts have been described upon the various mints, and the studies 
that have thus far been made upon these indicate an interesting 
evolution of the parasitic forms. The species referred to, however, 



4o8 



FUNGOUS DISEASES OF PLANTS 



is one of the most common, yet it may not be considered of any 
special economic importance. The aecidiospores are ahnost twice 
as long as broad, 40 X 1 7-26 /x. The uredospores are subspherical, 
and the teleutospores are conspicuous by their long, hyaline, and 
relatively thick pedicels, papillate apex, red-brown color, and verru- 
cose outer wall. 




Fig. 200. ^ciDiAL Stage of the Grain Rust on Barberry 



XIII. BLACK RUST OF CiRAIN 
Pucdtiia gramiuis Pers. 

BoLLEY, H. L., and Pritchard, F. J. Rust Problems. N. Dak. Agl. Exp. 

Sta. Built. 68: 607-672. Jigs. 1-30. 1906. 
Carleton, M. a. Cereal Rusts of the United States. Div. Veg. Phys. and 

Path., U. S. Dept. Agl. Built. 16: 1-73. pis. 1-4. 1899. 
De Bary, a. Neue Unters. iiber die Uredineen, insb. d. Entw. der Puccinia 

graminis u. d. Zusammenhang desselben mit Aecidium Berberidis. Monats- 

ber. K. Akad. d. Univ. Berlin (1865) : 15-49. pi. 11. 
Eriksson, J. Neue Unters. iiber d. specialisirung Verbreitung u. Hcrkunft 

des Schwarzrostes {Puccinia gniininis Pers.) Jahrb. f. wiss. Bot. 29 : 

499-524. 1896. 
Eriksson, J., und Hexxixc, E. Die Getreideroste, /. c. 
McAlpine, D. The Life-history of the Rust of Wheat. Dept. Agl. A'ictoria 

Built. 14: 1 89 1. 
Olive, E. W. Rusts of Cereals. S. Dak. Agl. Exp. Sta. Built. 109: 1-20. 

Jigs. /-J. 1908. 
Ward, H. Marshall. Illustrations of the Structure and Life-history of Puc- 
cinia graminis, the fungus causing the " Ru.st " of Wheat. Ann. Bot. 2 : 

217-222. pis. II, J2. 1888. 



PROTOBASIDIOMYCETES 



409 



Probably the most important species of the rust family, both 
from an economic point of view and also from the point of view 
of the development of mycological research, is the common species, 
Pitccinia graniiuis, upon cereals. It was upon this species that 
the classical researches of De Bary (1865 et seq.) were based, 
throwing light upon many phenomena of parasitism. In more 
recent times this species has 
served further as a means of 
developing a knowledge of 
biological and physiological 
forms, or specialized races. It 
has been the means, also, of 
showing the relation of the 
summer spore, or uredo stages, 
to the continual propagation of 
certain rust forms, and Eriks- 
son's mycoplasm theory sought 
evidence in phenomena ob- 
served in this species. 

Distribution and occurrence. 
It would appear that this fungus 
is distributed, in one or more 
of its numerous forms or races, 
throughout the world wherever 
certain grasses may be found. 

It is not in all regions the most common cereal rust, but in 
general it is so considered. The economic work upon rust fungi 
in such widely scattered and important cereal-growing countries 
of the world as Australia, Russia, Western Europe, and the 
United States has been largely concerned with this species. It is 
therefore the fungus which is commonly known as rust of wheat, 
oats, barley, and other cereals and many grasses. It is not at all 
restricted by minor climatic conditions, and in the United States 
it is found in its various forms upon certain grasses from the 
moist Atlantic seaboard to the most arid portions of the Great 
Plains, and from the Gulf Coast to the Great Lakes, The annual 
losses throughout the world amount to a stupendous figure, often 
estimated to reach one hundred million dollars. 




Fig. 201. Rust of Oats 



4IO 



FUNGOUS DISEASES OF PLANTS 



Host plants. It is scarcely possible to indicate all the various 
hosts upon which the species, in its various forms, has been re- 
ported. As mentioned above, however, it attacks all the more 
important cereals, — wheat, oats, rye, and barley, — together with 
ordinary grasses belonging to the same genera, in addition to such 
economic forms as species of Dactylis, Alopecurus, Agrostis, Poa, 
Phleum, Festuca, and numerous others. 

The important forms or physiological races of this species 
which have been thus far well established through experimental 
study are as follows : 

1. Secalis Eriks, & Henn. On Secale cereale, Hordciivi vul- 
gare, Agropyrnm repcns, Elyvius arenarhis, Bromns sccalums, 
and other hosts. 

2. Avenae Eriks. & Henn. Occurring on several species of 
Avena (including cultivated oats), Agrostis scabra, Alopecurus 
pratensis, Dactylis glomcrata, and other grasses. Nevertheless, 
there is some disagreement about some of the hosts upon which 
this form has been reported. 

3. Tritici Eriks. & Henn. On several species of Triticum (cul- 
tivated wheats), Hordeum, Agropyrum, and Elymus ; also some 
other grasses. 

4. Agrostis Eriks. On Agrostis caHina2Lnd Agrostis stolonif cm. 

5. Airae Eriks. & Henn. 

6. Poas Eriks. & Henn. on Poa coviprcssa. This form, however, 
requires further study in order to be sure that it is not more prop- 
erly one of those already indicated. 

The fungus. This species is of the type euheterouredo. The 
chief alternate host throughout its usual range is the common bar- 
berry {Berbcris vulgaiis). The life history of the fungus may be 
only briefly outlined, beginning with its appearance upon the bar- 
berry in the form of the spermogonial and cluster-cup stages. 

The mycelium is septate, considerably branched, and intercellu- 
lar. It gives rise, however, to small, very slightly differentiated 
haustoria, which penetrate the cells. The mycelium is distributed, 
in the case of the barberry, throughout various parts of the leaf. 
It is, however, in every case localized in areas within a definite 
range of the point of infection. In the development of the spore 
stages there is the usual sequence. The spermogonial stage appears 



PROTOBASIDIOMYCETES 



411 



first as small, flask-shaped bodies, shown in Fig. 202, breaking 
through the upper epidermis of the leaf. Somewhat later, and 
in the same spot, there appear on the under surface the aecidial 




Fig. 202. PucciNiA graminis. (After Ward) 
a, section of barberry leaf showing spermogonia and aecidia ; /;, jecidium 



Stage, which breaks through the epidermis in somewhat similar 
manner. The spermogonium shows a veiy simple development, 
resulting by the gradual growth in extent of a small mass of fila- 
mentous hyphae developing in an intercellular manner just beneath 



412 FUNGOUS DISEASES OF PLANTS 

the upper epidermis. At maturity the flask-shaped body consists 
of an indefinite wall, later giving rise to numerous filamentous 
branches within, most of which project inward toward the center, 
the majority bearing on their tips small rod-shaped or oval conidia. 
Other filamentous hyphas emerge from the mouth of the pycnidium 
as hair-like processes. The hyphae making up the pycnidium are 
all tinted yellow or orange in color, the coloring matter being first 
present in the protoplasm and later deposited in the cell walls. 
The spots in which first the pycnidia and later the aecidia are pro- 
duced are pale yellowish to orange in color, and the leaf is some- 
times considerably thickened. 

The aecidia are organized in the mesophyll tissue near the lower 
epidermis. In general, each aecidium is differentiated and developed 
following the formation of a weft of filamentous hyphal elements. 
According to Richards there is first formed at the base of the 
hyphal mass a well-differentiated short, thickened hypha. By the 
division of this hypha there arise numerous fertile branches, or 
young conidiophores, each of which originates a chain of spores. 
Every alternate cell in the chain becomes a perfect spore ; the 
others are small and temporary, remaining for a time as wedge- 
like structures between the spores. The outer border, or inclosing 
layer, consisting of differentiated hyphae, forms a definite peridium. 
Prior to the rupture of the epidermis, the fruit body has a more 
or less spherical form, and it consists merely of the sheath, or 
peridium, inclosing the numerous chains of spores. The increase 
in size of the spores breaks the peridium as well as the epidermis, 
and the aecidia appear superficially in the cluster-cup form (Pig. 
202). The spores there exposed separate readily and arc dis- 
tributed. The aecidiospores are more or less spherical and vary 
from 14 to 26 IX in diameter. This spore germinates, and upon the 
different grass hosts it penetrates the stomata, producing the my- 
celium of the uredo stage. 

The uredosori generally occupy linear areas, yet upon some 
hosts they may be in the form of small circular dots. They show 
a considerable amount of coloring matter when young, and when 
mature appear yellowish brown. They are ovate, 10— i 5 x 20— 35/x, 
with rather thick walls, the outer of which bears numerous echinu- 
lations or small spine-like appendages (Fig. 203, a). There are four 



I 



PROTC )BASI1)1()MYCETES 4 i 3 

germ pores meridionally disposed and opposite. Upon many hosts 
the uredospores are produced throughout a very long season. They 
may appear upon grain or blue grass in the early spring before the 
aecidiospore may be developed in the same region. In many cases 
it is evident that the rust may be propagated from year to year by 
continuous generations of the uredospores. Again, it has been 
experimentally shown that uredospores may retain the power of 



Fig. 203. PucciNiA gr.-iminis: Uredospores and Teleutospores 

germination for weeks. It is, therefore, generally possible to ac- 
count for the appearance of rust, even in spring grain, at a dis- 
tance from the alternate barberry host. In seeking to explain the 
infections in spring grain as due to the uredo stage from some 
neighboring grass stubble, it should be remembered that artificial 
inoculation experiments have shown a very definite restriction of 
hosts in the different physiological species. Some who have fol- 
lowed carefully outbreaks of rust in the grain fields, year after 
year in the Northwest, feel that the problem is not yet completely 



414 



FUNGOUS DISEASES OF PLANTS 



solved. The rust may appear, or seem to appear, in constantly 
increasing amount in a field repeatedly grown to wheat, other con- 
ditions apparently remaining the same, yet it is hardly possible to 
assume that wintered uredospores would explain such cases. 

The teleutosori are generally disposed in a linear manner on 
stems, leaves, and floral parts. They may arise, during the early 
part of the season, in the uredosorus, but as the plant matures, 
teleutospores alone are developed ; thus the black rust form is that 
most evident at harvest time and later upon the stubble. In gen- 
eral, the spores are somewhat spindle-shaped, or somewhat broader 
at the apex, deep brown in color, with a persistent pedicel (Fig. 
203,/;). They measure 35-60 x 12-22/i. One-celled spores are 
occasionally found. The teleutospores will not, as a rule, germi- 
nate with any degree of satisfaction until they have been exposed 
to outside conditions throughout a considerable portion of the 
winter. Germination has, however, been repeatedly followed, and 
in moist air the promycelium is typically four-celled, each produc- 
ing upon a fairly long sterigma the single sporidium (Fig. 203, b). 

XIV. RUST OF MAIZE 
Piiccitiia Sorg/ii Schw. 
Arthur, J. C. The /Ecidium of Maize Rust. Bot. Gaz. 38: 64-67. 1904. 

It is generally supposed that this fungus is a native of America, 
and that it may be regarded, so to speak, as an original corn {Zca 
mays) parasite. It is now certainly widely distributed in maize- 
growing regions, but is more abundant under conditions of relar 
tively high temperature. This fungus has also been reported on 
sorghum, but the maize fungus is distinct from Puccinia purpurea, 
now common in the southern United States and in the West Indies 
on certain species of sorghum. The uredospores are large, 23-30 
X 2 2-26 /i, and the teleutospores are smooth, 28-45 X 12-17/i, 
with a rather long and thick pedicel. 

On maize the rust affects particularly the leaves and leaf 
sheaths, but it may cause considerable damage to the develop- 
ment of the tassels. Nevertheless, it seldom amounts to an 
epidemic, and consequently has not received attention from the 
standpoint of control, or of varietal selection of the host. 



PROTOBASIDIOMYCETES 415 

The maize fungus has recently been connected with an /Ecidium 
{ALcidiiim Oxalidis Thiim.) on Oxahs, so that its heteroecism is 
estabhshed. This ascidial stage has seldom been found, and there 
is reason to believe that the uredo stage may commonly serve to 
carry the fungus over winter, 

XV. TIMOTHY RUST 
Puccinia Phhi-prataisis Eriks. & Henn. 

Eriksson, J., u. Henning, E. Die Hauptresultate einer neuen Untersuchung 
iiber die Getreideroste. Zeitsch. f. Pflanzenkr. 4: 140-142. 1894. 

Eriksson, J. Ueber die Specialisirung des Parasitismus bei den Getreiderost- 
piizen. Ber. d. deut. Bot. Ges. 12: 292-331 (cf. 309-316). 1894. 

Klebahn, H. Die wirtswechselden Rostpilze, /. <;., pp. 235-236. 

Timothy rust is common in Europe, occasionally damaging to 
a noticeable extent the cultivated timothy {Phleiun pratcnsc). It 
also occurs upon some other cultivated and native grasses. The 
fungus is unquestionably closely related to Puccinia gi-aminis, if 
not a form of this species. It is reported ineffective in producing 
the cluster cup of the barberry. During the past few years the 
timothy rust has been found in a considerable portion of the east- 
ern United States, although previously it had not been noticed, 
at least to any practical extent. It is not yet positive that the rust 
which occurs in America is the same as the European species. It 
is conceivable that the cultivated timothy has gradually become sus- 
ceptible to another form of Puccinia graviinis, but this remains to 
be determined by careful experimental work. The European rust 
has not been connected with an aecidial stage, and it has been 
shown that the uredospores are apparently capable of wintering 
over, and therefore the disease may be readily reproduced from 
season to season without an ascidial stage. If the appearance in 
America means a sudden introduction and rapid spread of the 
European rust, much damage may be expected from it. On the 
other hand, it may have been parasitic upon timothy for some 
time without having attracted attention. Experiments made by 
Eriksson in the open indicate that the rusts on timothy and 
meadow fescue are readily transferred from one of these hosts 
to the other, and with much less success to several other grasses 
employed in the experiments. 



41 6 FUNGOUS DISEASES OF PLANTS 

XVI. BROWN RUST OF WHEAT AND RYE 
Puccinia riihigo-vem De C. 

Eriksson, J. Ueber die Specialisirung des Parasitismus bei den Getreiderost- 

pilzen. Ber. d. deut. bot. Ges. 12 : 292-331. 1894. 
Freeman, E. M. Experiments on the Brown Rust of Bromes (Puccinia dis- 

persa). Ann. Bot. 16: 487-494. 1902. 
Ward, H. M. On the Relations between Host and Parasite in the Bromes 

[etc.]. Ann. Bot. 16: 233-315. 1902. 

Occurrence and nomenclature. The brown rust of wheat and 
rye is second only to the black rust in economic importance. In 
consideration of the detailed account of the black rust of wheat 
and other cereals and grasses, it will only be necessary in discuss- 
ing the brown rust to draw attention to the chief points of interest 
by way of comparison. Puccinia nibigo-vera occurs upon a variety 
of grasses besides wheats and rye, among these certain species of 
Bromus, Lolium, and Elymus. The aecidial stage was by De Bary 
determined to be a form on a borage, Anchiisa arvcnsis, known 
to occur also on AncJmsa officinalis. The nomenclature of this 
rust is complex, and at the outset it may be said that Eriksson 
and Henning distinguish under the above name two species, and 
they have abandoned the name Piicciiiia rnbigo-vcra De C. One 
of these species is denoted the yellow rust, and to it is applied an 
old name, Puccinia glumaruin (Schm.). The other species, desig- 
nated brown rust, is made a new species and called Puccinia dis- 
pcrsa. The last named is found by inoculation to be connected 
with the secidium on the borage hosts, while Puccinia gliDiiaruui 
is without known aecidial stage. 

At any rate, these forms have not been commonly distinguished 
in the literature, and Puccinia rubigo-vcra has been reported 
almost as widespread throughout the region of cereal production 
as the black rust. In the United States it is often unusually abun- 
dant in the central West. BoUey and others have shown that this 
fungus is able to carry itself through the winter by means of more 
or less continuous production of the uredo stage and by the my- 
celium in the leaves of winter grain. 

The secidia occur upon leaf blades, petioles, stems, and calyx of 
the borage hosts, producing rather conspicuous, bright yellow, 
slightly swollen spots. 



PROTOBASIDIOMYCETES 4 1 7 

It was very largely in characters of the uredosori and uredo- 
spores that there was found a means of distinguishing two species, 
or forms, as above mentioned. In the form Pucciiiia gluniaruvi 
the uredosori arp described as lemon-yellow, the sori united into 
long linear areas, while in the other form the sori are irregularly 
distributed over the whole surface and are described as brown- 
ocher in appearance. 

The teleutospores form sori which remain covered by the epi- 
dermis ; the one form is said to occur more upon leaf sheaths and 
stems, and the other upon the under surfaces of the leaves. 
Groups of teleutospores are arranged in fan-shaped masses sur- 
rounded by closely united, bent paraphyses. The spores are 
broader at the apex, irregular in form, more or less angular, 
generally 30-50 /x in length, and the upper cell 14-24/x broad. 

Both of the forms here mentioned are again divisible into 
several physiological races, each restricted to one or to relatively 
few hosts. 

XVII. RUST OF STONE FRUITS 

Pitccinia Pnini-spinoscT Pars. 

HOLWAY, E. W. D. North Amer. Uredinales 1 : 55-56. figs. 83 a, Sj b. 
McAlpine, D. Peach- and Plum-Leaf Rust. Victoria Dept. Agl. Guides to 

Growers 5 : 1-8. 1891. 
SCRIBNER, F. L. Leaf Rust of the Cherry, etc. U. S. Dept. Agl. Rept. (1887) : 

353-355- pt-3- 

This rust occurs throughout a considerable portion of southern 
North America. It is also found in Europe and Asia. It was in- 
troduced into Australia, apparently, somewhat earlier than 1883, 
and is now considerably distributed on that continent. 

This fungus has been found on various species of the genus 
Prunus in the central and southern United States. It is reported 
upon such hosts as the peach {Pi-?nnts Pcrsica) ; some of the native 
species of plum, such as Prunus avicricana and Prunus domcstica ; 
and on certain cherries, especially Prunus scivtina. In other sec- 
tions of the world it has also been noted on the almond [Prunus 
Amjgdalus), on the apricot {Primus armeniacd), and many other 
economic species. As a rule, this fungus is found upon the leaves, 
but it occurs also upon fruits of peach, almond, and apricot, and 
upon the stems of the peach under certain climatic conditions. No 



41 8 FUNGOUS DISEASES OF PLANTS 

striking discoloration of the leaves is produced at first, but the 
great number of sori which may be formed eventually give a 
light brown color to the leaf before it falls. Considerable defo- 
liation may result, and it is stated that a shot-hole effect is 
sometimes produced upon the almond. The fungus is much more 
destructive in relatively moist, warm climates. It appears gener- 
ally toward midsummer, but the most severe effects are commonly 
in the fall. 

It has recently been determined that the secidial stage of this 
fungus is Aicidhim piinctatiini. Tranzschel was able to produce 
the rust by inoculations from the aecidium above mentioned on 
Anemone eoronaria. These results were confirmed by Arthur 
with the aecidium from Hepatica acntiloba. This aecidium has a 
perennial mycelium in some of its hosts, so that this stage alone 
is believed to perpetuate itself. 

The uredospores occur upon all hosts of the genus Prunus 
mentioned. They are generally hypophyllous, minute, cinnamon- 
brown, and may be so numerous as practically to cover the entire 
leaf. The spores are light brown, generally ovate or elliptical, 
with thickened apex. They are thickly verrucose and are pro- 
vided with from two to three equatorial germ pores. They measure 
20-36 X 14-20/L1. Paraphyses are abundant. Tranzschel deter- 
mined that uredospores kept over winter at St. Petersburg were 
capable of germination the following spring. 

The teleutospores generally appear in small groups among the 
uredospores and later supplant these entirely. The pustules are 
generally pulverulent and chestnut-brown. The teleutospores are 
from very light to reddish brown upon the different hosts. In 
general form they are elliptical, deeply constricted, and the two 
cells are more or less equal, often subspherical. They separate 
readily. These spores are provided with pointed tubercles. The 
spores measure 32-44 x 20-26 /x. The pedicels are slender, hya- 
line, and fragile. The lower portions of these become agglutinated 
into short columnar masses. The free portion of each pedicel is 
usually about the length of the spore. 



rR( )'r( ) BA S 1 1 ) I O M \C KTES 



419 



XVIII. HOLLYHOCK RUST 

I^ituiiiia ))ialvaccanim Mont. 

DUDLKV, A\'. R. The Hollyhock Rust. Cornell Agl. Kxp. Sta. liullt. 25: 
154-155. 1.S90. 




Fig. 204. PucciNiA malvacearum : Rust of Hollyhock. (Photograph by 

H. H. Whetzel) 

The hollyhock rust is known to infest a large number of genera 
and species of the mallow family (Malvaceae). It is at present widely 
distributed throughout a large portion of the world, and is in the 
United States most important on the cultivated hollyhock {Althcea 



420 



FUNGOUS DISEASES OF PLANTS 



7-osca). The fungus is apparently a native of Chile and was not 
found in central Europe until between 1873 and 1877. It was 
evidently introduced into the United States prior to 1886 and 
has received special attention since about 1890. 

On the hollyhock the fungus commonly occurs in such quantity 
that the proper development and normal functions of the leaves 
may be seriously inhibited. The sori are most abundant on the 
under surfaces of the leaves (Fig. 204), but they also occur upon 
other parts. They are at first small and circular in outline, but 
may become confluent over considerable areas. 

During favorable conditions the teleutospores germinate im- 
mediately, and there is no evidence that the mycelium is gener- 
ally perennial. Nevertheless, Fischer believes that in temperate 
climates the wintering over is ordinarily effected by means of 
teleutospores which fail to germinate on account of being over- 
taken by unfavorable conditions. The spores are light colored 
and measure 17-24 x 35-63 /x. They are often spindle-shaped, 
and the pedicel is long, frequently from 100 to 130/i. 

This disease has been fairly well controlled by the destruction 
of diseased portions of plants and by spraying v/ith Bordeaux 
mixture. 

XIX. PUCCINIA: OTHER SPECIES 

Puccinia Helianthi Schw. This euautouredo occurs commonly 
upon numerous species of Helianthus, including the sunflower 
{Helianthus anniiiis). Recent experiments indicate that the form 
on HcliantJius Uibci'osus is at least physiologically distinct, and 
doubtless the species may be broken up into many forms. Puc- 
cinia Helianthi (with all spore stages) is distinguished from Puc- 
cinia Tanaccti, a related but apparently imperfectly known species, 
by the smooth apex of the teleutospore and the presence of only 
two germ pores in the uredospores. 

Puccinia coronata Cda. This species has an aecidial stage upon 
the buckthorn (Rhamnus). At maturity the groups of cluster cups 
are very conspicuous by the color and also by the deformities. The 
aecidiospores measure 18-25 X 14-19/^. The uredo and teleuto 
stages are common upon oats, and on such cultivated grasses as 
Dactylis glomerata and Festnca sylvatica. The uredosori are 



PROTOBASIDIOMYCETES 42 1 

bright yellow, the spores ovate, with roughened surfaces, measur- 
ing 28-32 X 20-24 /x. The teleutosori remain covered by the epi- 
dermis, and the spores are notably distinctive in being cuneate in 
form, with several horn-like projections on the thickened apex, and 
with a very short pedicel. This species has also been broken up 
into diverse forms, some of which are considered distinct species. 

Puccinia Chrysanthemi Roze. The chrysanthemum rust ^ has 
been of some consequence in Europe and America during the 
past fifteen years. It was common in Japan at a much earlier 
time. The principal hosts are CJirysanthcvimn indicinn and 
CJirysanthcmum sinctisc. In the warmer coastal regions of Japan 
and in Europe and America continuous generations of uredo- 
spores may be produced. In these places teleutospores occur 
rarely. When they occur, mesospores and irregularly formed 
uredospores are also common. In the cooler portions of Japan 
teleutospores are commonly found in the autumn. It would ap- 
pear that uredospores and teleutospores are the only stages in the 
normal life cycle of this species. In greenhouse culture this rust 
is generally controlled by resistant stock and care in watering. 

Puccinia Tragopogi (Pers.) Cda, This species, occurring on 
members of the genus Tragopogon, and especially on the culti- 
vated form, Tragopogo7i porrifolius, is not uncommon in gardens 
where salsify is annually grown. It is constantly without uredo- 
spores and exhibits the anomalous condition of producing also 
unicellular teleutospores. There is, moreover, great variability in 
the size of this spore form. 

Puccinia suaveolens (Pers.) Rostr. The characteristic odor, or 
aroma, of the spermogonia is a distinctive peculiarity of this species. 
It is considered to be a means of attracting insects, perhaps for 
purposes of distribution. It will be recalled, however, that the sper- 
matia are not known to be at present effective in the propagation 

1 Arthur, J. C. Chrysanthemun Rust. Ind. Agl. P^xp. Sta. Built. 85 : 143-150. 
1900. 

Jacky, E. Der Chrysanthemum-Rost. Zeitsch. f. Pflanzenkr. 10 : 132-142. 
1900. 

Kusano, S. Biology of the Chrysanthemum-Rust. Built. Coll. Agl. Imp. Univ. 
Tokyo 8 : (reprint i-io). 1908. 

Roze, E. Le Puccinia Chrysanthemi, etc. Bull, de la Soc. Myc. de France 16 : 
88-93. 1900- 



42 2 FUNGOUS DISEASES OF PLANTS 

of any rust. The spermogonia are extremely numerous, cover- 
ing practically both surfaces of the leaf, while the uredo and 
teleutosporic sori occur on the under surface of the leaves only. 
In the first generation the sori are confluent, but in the second 
generation distinct. This species occurs on the common Canada 
thistle {Cirshirn arvense). Infection from the teleutospores pro- 
duces a mycelium which deforms the host, but the infection from 
uredospores produces a localized mycelium. These differences upon 
the same host suggest a condition which may be regarded as bio- 
logically intermediate between true autoecism and heteroecism. 

Puccinia Hieracii (Schum.) Mart. This rust occurs on various 
species of Hieracium, and from the observations made it would 
also appear to be a species embracing many different forms. 

Puccinia fusca Relhan. This rather variable species is parasitic 
upon certain anemones, and the mycelium has been experimentally 
determined to be perennial in the host, 

XX. GYMNOSPORANGIUM 

Farlow, W. G. Notes on Some Species of Gymnosporangium and Chryso- 

myxa in the United States. Proc. Amer. Acad. Arts and Sci. 20 : 3 1 1-323. 

.1885. 
Farlow,W. G. The Development of the Gymnosporangia of the United States. 

Bot. Gaz. 11 : 234-241. 1886. 
Farlow, W. G. The Gymnosporangia (Cedar-Apples) of the United States. 

Anniv. Mem. Boston Soc. Nat. Hist. 38 pp. 2 pis. 1880. 
Pammel, L. H. The Cedar Apple Fungi and Apple Rust in Iowa. lowaAgl. 

Exp. Sta. Built. 84: 1-36. 1905. 
Richards, H. M. The Uredo-stage of Gymnosporangium. Bot. Gaz. 14 : 

21 1-2 1 6. pi. ly. iSSg. 
Thaxter, R. Notes on Cultures of Gymnosporangium made in 1887 and 

1888. Bot. Gaz. 14: 163-172. 1889. 
Thaxter, R. The Conn. Species of Gymnosporangium (Cedar-Apples). 

Conn. Agl. Exp. Sta. Built. 107: 1-6. 1S91. 

There is, perhaps, no genus of rust fungi comprising several or 
more species which is as uniform in developmental processes as 
the genus Gymnosporangium. Aside from a direct agreement in 
the sequence of spore forms, and in the general relations of these 
forms one to another in the different species, all have the same 
spore forms, namely, spermogonia, secidia, and teleutospores ; and 
in the different species the same spore forms appear in almost 
the identical season. 



PROTOBASIUIOMYCETES 423 

There are about fifteen species of these fungi, all but one of 
which have the ascidial or rust stage (Roestelia) on some member 
of the tribe Pomccie, generally apple, pear, or crab (Pyrus), cjuince 
(Cydonia), shad bush or service berry (Amelanchier), or hawthorn 
(Crataegus). The teleutosporic stage, which is commonly produced 
on hypertrophied parts in the nature of " cedar apples," witches' 
brooms, and other deformities of the host, generally occurs upon 
one of the species of red cedar or juniper (Juniperus) ; only two 
species of these fungi are exceptions, these having as a host the 
related genus Cupressus. These fungi are of economic interest 




Fig. 205. .EciDiAL Stage of Gymnostorangium on Fruit of IIaw 

because of the injuries to fruits and leaves of the Pomeae, and 
not as a rule because of serious injuries to the coniferous hosts. 

On account of the great similarity in development, the general 
facts of life history import may be collectively presented. More- 
over, since in the order of season the teleutosporic form occurs 
first, the discussion will follow this plan. 

Soon after the growing season begins, and following a warm 
rain, there will be found protruded from the cedar apples, or from 
enlargements on the twigs of other conifers mentioned, gelatinous, 
orange-colored spore masses, sometimes horn-like, and again almost 
shapeless. These masses consist, in large part, of orange-tinted 



424 



FUNGOUS DISEASES OF PLANTS 



teleutospores with long, gelatinizing pedicels (Fig. 206). These 
teleutospores germinate immediately. Three promycelia often 
arise from a spore, each through a germ pore situated near the 
septum between the two cells. The promycelium may form four 
sporidia in the usual manner, and these sporidia 
cannot reinfect the cedar. They may apparently 
be borne long distances by the wind. Moreover, 
they are produced during the season when young 
leaves and fruits are abundant on the apple, 
quince, and such plants. Falling upon the con- 
genial host, the spore immediately germinates, 
and infection is secured. In time the rust stage 
of the fungus appears. This stage consists of 
spermogonia and aecidia. It is then perhaps mid- 
summer, and the abundant aecidiospores return 
the fungus to the conifer host, where in time a 
gall or a deformity is again produced. 

The rust spots on the pomaceous hosts appear 
at first as clear yellow or orange areas, slightly 
thickened or raised. Soon a papillate appearance 
indicates the presence of the spermogonia or pyc- 
nidia, which are all of a characteristic, simple 
type. The aecidia follow in a brief period on the 
under side of the leaf, or covering large areas on 
the fruit (Fig. 205), The aecidium (rcestelia) is an 
organ of some length, appearing cylindrical or 
jug-shaped after emergence. A circular orifice 
is developed, and the peridium breaks into a 
characteristic margin, sometimes fimbriate. The spores, which 
are produced in chains, break apart when mature. They also 
germinate immediately. 

Control consists primarily in the removal of the cedars, if that 
is practicable. Attention should also be paid to the resistance of 
varieties of apples grown. It is, moreover, of some value to spray 
with the standard Bordeaux mixture at about the time of ripening 
of the teleutospores. 




Fig. 206. GvMNo- 

SPORA.VG/UM A/.-t- 

cROPUs: Teleu- 
tospores 



PROTOIJASIDIOMYCETES 



425 



XXI. CEDAR APPLES AND APPLE RUST 

G\)nnos[>omngiHni macropiis Lk. 

This is one of the most widespread and economically important 
of this <;enus. It produces the large cedar apples on Jiiiiipcrus 
virginiana (l^'ig. 207). This fungus occurs practically throughout 




Fig. 207. GYMxosroR.txGirM m^icroits: Cedar Apple 

the range of the red cedar and its other hosts. The secidial stage 
occurs on the apple {Pjrus Mains) and also on Pynis coronaria, 
and was originally described as Rtvstclia Pyrata (Schw.) Thaxter, 
On the leaves some injury is done to these plants when the 



426 FUNGOUS DISEASES OF PLANTS 

infection is severe, but it is upon the fruit that the fungus be- 
comes, in many sections of the United States, a serious disease. It 
is far more common in regions of considerable humidity, but owing 
to the fact that teleutospores are produced during wet weather, infec- 
tion is usually immediately assured upon the pomaceous hosts in 
the vicinity. The fungus has been noticeably abundant in apple- 
growing regions in the eastern Appalachians and in the South. 
Varieties of apples differ greatly in their susceptibility. In the far 
West, crosses between the wild crab apple and the cultivated species 
have given some forms peculiarly susceptible. The gall formation 
on the cedar commonly attains a diameter greater than 2 cm., and 
when the horn-like gelatinous sori are developed, the mass from 
edge to edge may measure 8 cm. The teleutospores are 46-60 x 
15-20/A. 

XXII. GYMNOSPORANGIUM: OTHER SPECIES 

Gymnosporangium clavariaeforme (Jacq.) Rees is a species un- 
usually abundant in the northeastern United States. The teleuto- 
sporic form occurs on the common or dwarf juniper {Junipcrus 
cojiiiiiimis). Slight enlargements of the twig are produced, and the 
sori are orange-red in appearance. In America the ascidia occur 
on the hawthorn {Cratagns tonicntosd), while in Europe they are 
also produced upon Cratagus oxyacantha, Cratagiis moiiogyna, 
PyTus comviujiis, and occasionally other pomaceous trees. This 
species is apparently not so fixed in its specialization with respect 
to hosts for the ascidial stage as other members of this genus. 

Gymnosporangium globosum Farl. This species produces on 
the red cedar {Junipcrus virginiaua) smaller cedar apples than the 
preceding, and they are also distinguished from the latter by the 
texture of the gall, the deeper color of the spore masses, and cer- 
tain spore characters. 

This fungus is a chief cause of the apple rust of the New 
England States, and the rcestelia stage is also found on the pear, 
quince, and some varieties of mountain ash. 

Gymnosporangium Sabinae Plowr., which is closely related to 
Gyinnosporauginm globosum, has also the same coniferous host. 
The aecidial stage has for some time been recognized as injurious 
to pear culture in Europe. 



PROTOBASIDIOMYCETES 427 

XXIII. ORANGE RUST OF RASPBERRY AND BLACKI5ERKY 
Gymnoconia Peckiana (Howe) Tranz. 

Clinton, G. P. Orange Rust of Raspberry and Blackberry. 111. Agl. Exp. 

Sta. Built. 29: 273-296. ph. 1-4. 1893. 
Farlow, W. G. Notes on Some Species in the Third and Eleventh Centuries 

of Ellis's North American Fungi. Proc. Amer. Acad. Arts and Sci., N. S. 

18: 65-85(76). 1883. 
Newcombe, F. C. Perennial Mycelium of the Fungus of Blackberry Rust. 

Journ. Mycology 6: 106-107. ph. ^,6. 1890. 
Richards, H. M. On the Development of the Spermogonium of Casoma 

nitens (Schw.). Proc. Amer. Acad. Arts and Sci., N. S. 20 : 30-36. pi. i. 

1893. 
Tranzschel, W. Culturversuche mit Casoma interstitiale Schlechtd. (= C. 

nitens Schw.). Hedwigia 32 : 257-259. 1893. 

Occurrence and symptoms. The orange rust is a common disease 
of black raspberries and blackberries throughout portions of the 
United States and Canada, and it is also widely distributed in 
Europe and Asia. It is found upon various species of the genus 
Rubus, whether wild or cultivated, although there is considerable 
difference in the susceptibility of different varieties of the same 
species. Among raspberries Clinton has cited the Kittatinny as 
perhaps the worst affected, and the Snyder as notably resistant. 
In other regions, however, the latter has proved less resistant. 
The fungus may be noted almost as soon as the young leaves be- 
gin to appear in the spring. The spermogonial stage appears first 
and gives to the surface of leaves and even young stems a glandu- 
lar appearance, which may often be mistaken for a natural condi- 
tion. A comparison, however, of affected with unaffected plants 
readily demonstrates the specific effects of the fungus. At times 
the spermogonia are, however, limited in distribution, affecting only 
a portion of the leaves of a bud, or merely small areas upon a 
single leaf. In from ten to fifteen days after the appearance of 
the spermogonia the striking aecidial stage may be found appear- 
ing only on the lower surface of the leaf. The cushions which 
produce the spores are rapidly developed beneath the epidermis, 
and upon the rupture of the latter the bright orange spores are 
disclosed. Eventually the under surfaces of the leaves may ap- 
pear to be covered with a continuous mass of more or less adhe- 
sive orange-red material. All of the vegetative parts of the plant 
which are affected are usually greatly impaired in vitality and 



428 



FUNGOUS DISEASES OF PLANTS 



frequently appear spindling from the beginning. Nevertheless, the 
affected shoots or canes may not be killed, and the disease may 
reappear upon such affected plants the following year from the 
growth of the mycelium into young shoots. In the end, practically 
all affected plants are killed, and their vitality is from the outset 
so diminished that productiveness is impossible. 




Fig. 208. Blackberry Rust, C^oma Stage 
To the left, normal shoots ; to the right, diseased 

The fungus. The mycelium of this fungus has been carefully 
studied in the growing canes. It is intercellular, and grows rap- 
idly in the direction of formative tissues, or where new cells are 
being produced, extending but slightly into tissues or organs which 
have matured. The mycelium is richly provided with haustoria. 
The tip of the haustorium enlarges as a knob-like organ, and this 
is commonly more or less in contact with the cell nucleus. The 
mycelium in the root penetrates the parenchymatic cortical cells, 



PR()T()11\SI I )I( JMYCETES 



429 



and in the regions where the hyphae are abundant the amount of 
starch is distinctly less than in those not pervaded by the fungus. 
In the stem, according to Clinton, the mycelium is found espe- 
cially in the pith, in a more or less zonal area situated near the 
fibrovascular system. The young mycelium is more readily seen 
on account of the greater amount of coloring matter which it 
contains. 

The structure of the spermogonial stage has been carefully stud- 
ied by Richards. His work indicates that the spermogonia arise as 
a bundle of septate threads which press against the surrounding 




a h 

Fig. 209. C^oMA Stage of Gymnoconia Peckiana. (After Clinton) 
a, general effect on leaf ; b^ cross section through a young sorus 



cells so as to cause them to collapse, and these injured cells are 
finally penetrated by the mycelium. On reaching full growth small 
spore-like bodies are abscised from the ends of each thread ; and 
when produced in quantity, the epidermis is ruptured, or punctured, 
and the spores ooze out as a small glandular droplet. It has not 
been shown with certainty that these spores have been germinated. 
The observations upon a budding habit suggested by early ob- 
ser\'ers may have concerned themselves with yeast cells asso- 
ciated with the spores and accidentally introduced into the culture 
drop. 



430 



FUNGOUS DISEASES OF PLANTS 



The gecidial or caeomal stage may cover practically the whole of 
the lower surfaces of the leaves. This stage is the one of great im- 
portance from the standpoint of the propagation or dissemination 
of this fungus. In the formation of the spores extensive mycelial 
cushions are developed near the lower surface of the leaf, and from 
these cushions there arise cells perpendicular to the surface, which 
elongate, and in time originate chains of the aecidiospores. The 
development of these spores effects a rupture of the epidermis, so 
that the mature spores are exposed (Fig. 209). The maturity of the 
spore involves the development of a considerable amount of color- 
ing matter in the protoplasm, so that when the spores are exposed, 
the under surface of the leaf is bright orange. The spores are 
ordinarily ovoidal or more or less globose, sharply verrucose, and 
measure 12-24X 18-32/11. Germination may take place immedi- 
ately upon maturity of the spores, and the Rubus hosts may be 
promptly infected. The lack of a true peridium in this stage is the 
chief reason for separating the species generically from species of 
Puccinia. 

The teleutosporic form of this species is of the Puccinia type. 
Prior to the experiments of Tranzschel and Clinton, working inde- 
pendently, it bore the name Pucciiiia Pcckiana. The teleutosporic 
form is relatively far less abundant than the other stages. The chief 
peculiarity is found in the location of the germ pore in the basal 
cell, which is always considerably below the dividing wall. 

XXIV. RUST OF ROSES 

Phragmidiiim siibcorticiitin (Schrank) Wint. 

Bandi, W. Beitrage zur Biologic der Uredineen (Teil I). Hedwigia 42: 
1 18-136. 1903. 

The various species of Phragmidium are parasitic upon different 
rosaceous hosts. No species of these rusts produces any very 
serious disease of a cultivated variety ; nevertheless, consideration 
should be given to a general study of one member of this genus. 
The fungus above indicated occurs commonly in moist regions 
upon several wild roses. Spermogonia and aecidia (caeoma type) 
arc produced on the stems, petioles, leaf veins, etc., as orange- 
red pustules, sometimes inclosed by paraphyses. The spores are 



4 



PROTOBASIDIOMYCETES 



431 



produced in short chains and measure 24-28 x 1 8-2 1 /i (Fig. 210,/;). 
The uredesori occur on the under surface of the leaf. They are 
somewhat hghter colored than the caeoma and are constantly 
inclosed by paraphyses. Individual spores are about the same in 
size and form, however, as the previous type (Fig. 210, c). In the 
same sori with the latter may be produced also the teleutospores. 





Fig. 210. Phragmidium suBcoRTiciuM 
a and </, caeoma and teleuto stages on rose ; /', c, and e^ spore forms 

usually in small black groups. A teleutospore is more or less 
spindle-shaped, usually six to eight cells in extent (Fig. 210, c), and 
each cell is provided with several germ pores. The outer wall of 
the spore is generally uneven or warty toward the apex, and 
there is a distinct terminal papilla. The teleutospores measure 
65-100 X 30-45 /A without the pedicel. The pedicel is persistent, 
swollen at the base, and about as long as the spore. The cells of 
the teleutospore adhere closely, while in some other species they 
separate readily on maturity. 



432 FUNGOUS DISEASES OF PLANTS 

XXV. RUST OF RHODODENDRON AND NORWAY SPRUCE 
Chrysomyxa Rhododendri (De C.) De Bary 

Occurrence. The rhododendron rust is especially abundant in 
portions of Europe and America, particularly in regions where the 
wild species of the rhododendron and of the fir grow together in 
the same forest areas. In fact, the rust is the most common fun- 
gus of the rhododendron, and in regions where the fir abounds 
the rhododendron is seldom free from its attacks. In Europe it is 
notably abundant on Rhododejtdron Jiirsutjtiii and on Rhododendron 
fcrruginenm, these being the hosts upon which the uredo and 
teleuto stages are found. The spermogonial and ascidial stages 
are confined to the fir {Picca cxcclsd). In the United States this 
fungus is particularly common in the mountains of the East, and 
southward as far as the southern limits of the Appalachians. 

The spore forms. The spherical spermogonia appear upon 
young leaves of the fir in the spring, and these are followed a 
month or more later, sometimes as late as midsummer, by the 
aecidial stage. The aecidia break through the epidermis of the 
leaf as more or less tuberculate structures arising thickly on 
the under surfaces of the leaves to a height of two or three milli- 
meters, each producing numerous secidiospores. The latter germi- 
nate readily, and the host is penetrated by means of the stomata. 
It is claimed that the mature leaves of the rhododendron are those 
generally infected. The mycelium developed in such persistent, or 
evergreen, leaves winters over and produces abundantly the uredo 
stage, followed also by the teleutosporic stage. The uredo stage 
serves to spread rapidly the fungus from one plant to another 
during the growing season. The teleutosporic stage, however, ger- 
minates immediately, and the basidiospores penetrate the young 
shoots of the fir, thus completing the life cycle of this euheterouredo. 
The uredosporic pustules appear only on the under surfaces of the 
leaves, or occasionally on the younger stems, and these spores are 
borne in chains with alternate sterile cells. The teleutospores are 
closely adherent in groups. They are more or less cylindrical in 
form, extremely light in color, and vary as to the number of cells 
from three to six, those at the center of the group showing the 
larger number of cells. 



PROTOBASIDIOMVCETES 433 

Control. No attempts have been made to control this disease, 
and it is doubtful if any effective method could be found, except 
that of excluding one or the other of the two hosts from any 
particular region. It is, moreover, possible that the uredo stage 
may serve to transmit the disease from season to season upon 
the rhododendron. 

XXVI. THE EUROPEAN CURRANT RUST 
Cronartiiim Ribicola Fisch. de Waldh. 

Henxixgs, p. Beobachtungen iiber das verschiedene Auftreten von Cronar- 
tium ribicola Dietr. auf verschiedenen Ribes-Arten. Zeitschr. f. Pflanzenkr. 
12: 129-132. 

Klebahn, H. Ueber die Formen und den Wirthswechsel der Blasenroste 
der Kiefern. Ber. d. deut. bot. Ges. 8: (59)-(70). 1S90. 

Klebahx, H. Neue Untersuchungen und Beobachtungen iiber die Blasen- 
roste der Kiefern. Hedwigia 29 : 27-35. 1890. 

Plowright, C. B. P"ungus on Weymouth Pine and on Currants, (iard. 
Chron. 12(111): 44. 1S92. 

Stewart, F. C. An Outbreak of the European Currant Rust. N. Y. Agl. 
Exp. Sta. Tech. Built. 2 : 62-74. P^^- ^S- 1906. 

v. TuKEUF, K. Infektionsversuche mit Peridermium Strobi, dem Blasenroste 
der Weymouthskiefer. Arbeiten aus der Biolog. Abt. f. Land- u. Forst- 
wirtschaft am Kaiserl. Gesundheitsamte 2: I73-I75- I9°i- (Abstract 
in Centrbl. Bakt. u. Parasit. 7 (Abt. II): 445.) 

Occurrence. Until within the past few years this fungus was 
known to be of importance only in Europe, and indeed as yet 
only sporadic cases have been found in other parts of the world. 
At Geneva, N. Y., there was an outbreak on currants during 1906, 
and special measures were taken to stamp out the fungus in that 
vicinity. It appears also that the fungus is known in India. The 
aecidial stage of this fungus was named Pc?idcrminin Strobi, by 
Klebahn, but inoculation experiments made subsec^uently both by 
the author of this species and by others have demonstrated its con- 
nection with the uredo and teleuto forms found on currants. The 
secidial stage has been reported most destructive to the white pine 
{Pvms strobiis) in many parts of Europe. The injuries caused 
by the uredo and teleuto stages upon the currant are, however, not 
of sufficient importance, of themselves, to arouse particular in- 
terest. In this connection it is instructive to note that the white 
pine is a native of America ; and it seems remarkable, when the 
susceptibility of this species in Europe is considered, that the 



434 



FUNGOUS DISEASES OF PLANTS 



fungus should not long ago have appeared in America.^ The 
aecidial stage is also found upon another species of pine, Pinus 
ccnibra, and it is believed by some that the fungus is indigenous 
upon this species in Russia and in Switzerland. 

Host plants. The uredo and teleuto stages (Fig. 211) occur 
upon many varieties of the genus Ribes, representing several 





Fig. 211. Cronartium Ribicola 

a, sori on currant leaf ; b, sorus and teleutosporic column ; c and d, 
uredospores and teleutospores 

1 During June, 1909, the aecidial stage of this fungus was found in a nursery 
of three-year-old white pine seedlings imported from Germany. Many seedlings 
of this importation have been distributed to several northeastern states and to 
Canada. A determined effort is being made to inspect all plantings, to destroy 
the diseased stock, and also to prevent further importation of the infected white 
pine seedlings. Inspection of such seedlings at the time of importation is prac- 
tically valueless, since the fungus has an incubation period in the bark of nearly 
one year before the characteristic swellings appear. Details of the outbreak in 
New York are discussed in the following articles : 
Atwood, G. G. Blister Rust of Pines and the European Currant Rust. Dept. 

Agl., State of N. Y. Hort. Built. 2 : 1-15. 1909. 
Spaulding, Perley. European Currant Rust on the White Pine in America. 
Bur. Plant Ind., U. S. Dept. Agl. Circular 38 : 1-4. 1909. 



PROTOBASIDIOMYCETES 



435 



different species. According to Stewart forty-eight out of fifty-four 
varieties of currants were affected in one plantation in the Geneva 
outbreak, representing the three species Rilyes nignnn, Ribcs rii- 
hrum, and Ribcs aurcuni. The only varieties which were free 
from the fungus in this attack were the following : I^rince Albert, 
Gondouin White, Stultz, and an unknown variety, all of Ribcs 
rubnnn, and Crandall and Utah Golden of Ribcs auiruvi. In 
another plantation where sixteen different species of Ribes were 
cultivated, only one species, Ribcs irrigiunn, was rusted, but these 
plantations did not include Ribcs nignnn and Ribcs rub^imi. 

Control. In attempting to control or stamp out this disease, it 
would seem, with the information at hand, that the only hope 
would lie in the destruction of one or the other of the two hosts, 
the currant or pine. It is assumed in this connection that the 
two host plants are invariably essential to the maintenance of the 
fungus. Since the fungus appears to be of little importance as a 
disease of currants, the growers of this fruit evidently will not re- 
sort to heroic measures, and it will devolve upon foresters to watch 
closely for the fungus, and if it appears, eliminate the wild species 
of Ribes from the forest area. 

XXVII. ORANGE RUST OF ASTER AND GOLDEN-ROD 
Coleosporium Solidaginis (Schw.) Thiim. 

Arthur, J. C., and Kern, F. D. North American Species of Peridermium. 

Built. Torrey Bot. Club 33: 403-438. 1906. 
Clinton, G. P. Peridermium acicolu?/!, the ^cial Stage of Coleosporium 

Solidaginis. Science 25 : 289-290. 1907. 
Clinton, G. P. Hetercecious Rusts of Connecticut having a Peridermium 

for their yEcial Stage. Conn. Agl. Exp. Sta. Rept. (1907): 369-396. 

pis. 23-32. 

Occurrence. Of the several species of Coleosporium having 
uredospores and teleutospores on species of Compositae, there is 
none of such common occurrence throughout North America as 
the species here discussed. To this species are referred the orange 
rusts of many species of Aster and Solidago (golden-rod). It in- 
cludes also as hosts representatives of several other genera, among 
which is the cultivated aster {Callistcphns Jwrtensis). This fungus 
is by many regarded as identical with a species occurring wide- 
spread in Europe upon Senecio. 



436 



FUNGOUS DISEASES OF PLANTS 



1 



The genus Coleosporium is to be considered entirely heteroe- 
cious, and whenever aecidial stages are known in the hfe cycle, 
they occur on species of Pinus, and are referable to the form 
genus Peridermium, 

The aecidial stage of the species here discussed has recently 
been found through inoculation experiments to be a form known 

a s Pe ride rm i u m 
acicohmt occurring 
on leaves of Pinus 
rigida in several 
of the northeastern 
states. The Euro- 
pean form occurs 
upon branches and 
stems of Pinus 
sylvcstris. 

The fungus. The 
uredo and teleuto 
stages are merely 
conspicuous by 
their color, and in 
this particular in- 
stance the aecidial 
stage is by no 
means striking. 
Other forms or 
species of Peri- 
dermium, however, 
may produce considerable swellings upon their hosts. 

According to Clinton the infection of young pine leaves may 
take place in spring, the aecidia resulting the following year. It 
would appear that the Peridermium is inessential for the continu- 
ous propagation of the rust upon composites in the United States, 
since the uredo stage is produced practically throughout the winter 
on leaves of the basal rosettes. 

The spermogonia appear upon the needles in autumn, but the 
aecidia are not developed until spring. They occur on both sur- 
faces of the leaves in slightly discolored spots. They are crumpent, 




Fig. 212. Peridermium on Piine. (After Hartic 



PROTOBASIDIOMYCETES 



437 



tongue-shaped bodies .5-./ mm. high, opening by an irregular rup- 
ture of the peridium. The spores are, according to Arthur, coarsely 

verrucose with deciduous tuber- 
cles, except along one narrow 
line, where tubercles fail. 

The uredospores are produced 
in orange-yellow sori, which soon 
fade to nearly white. They are 
generally ellipsoidal, measuring 
27-30 X 1 7-22 /x. The teleuto- 
spores are borne in crowded 
waxy masses, and are at maturity 
a chain of four basidial cells within 
a somewhat gelatinized common 
wall. They are sessile, 5 5-80 x 
I 5-23 /u., and the cell wall at the 
apex is generally swollen, often 




h a 

Fig. 213. CoLEospoRiu:\i Senecionis 

{b after Tulasne) 



attaining a maximum thickness 



of 30-40 /x. 



XXVIII. RUST OF POPLAR 

Melampsom tre/iii/he Tul. 

Tulasne applied the above name to a rust of the poplar {Popuhis 
t re HI N la) occurring throughout a considerable range in Europe. 
It would seem 
that this name 
would now in- 
clude at least 
three forms, or 
species, as dis- 
tinguished by 
Klebahn, viz., 
Melampsora Pinitorqua 
Rostr,, Melampsora 
Lariei-t rem nice Kleb., 
and Melampsora Mag- 
misiana Wagn, These 




Fig. 214. Melampsora tremul^ : Uredospores 

AND TeLEUTOSPORES 



438 FUNGOUS DISEASES OF PLANTS 

three forms, together with one discussed by Klebahn as Melainp- 
sora Rostriipii Wagn., all agree in having more or less spherical 
uredospores, and in no case are there marked morphological dif- 
ferences in the uredospores or teleutospores within this group. The 
caeoma stages have, however, been determined, for these forms, to 
occur respectively upon Pinus, Larix, Chelidonium and Corydalis, 
and Mercurialis. For our purpose, it does not matter particularly 
whether these forms are considered a group of closely related 
species, or merely well-established physiological forms of a single 
variable species. In Europe these are found chiefly upon Popiihis 
tremida and Popidiis alba. In the United States it would seem 
difficult at the present time to name the hosts positively, although 
Popiibis trcnmloides may be specially mentioned. 



CHAPTER XV 

AUTOBASIDIOMYCETES 

In this class the sporophore or mycehal body may be of most 
diverse form. The most essential character, however, is that ordi- 
narily a portion of the sporophore is eventually differentiated into 
a close layer, the hymenium, from which arise, in a palisade man- 
ner, clavate or cylindrical basidia. Each basidium produces four 
(occasionally two, six, or eight) unicellular basidiospores, each on 
a relatively short sterigmatum. The fruit body, or sporophore, may 
reach, in this class, the maximum size and complexity attained 
among fungi. 

I. EXOBASIDIALES (EXOBASIDIACE^) 

Brefeld, O. Die Gattung Exobasidium. Unters. a. d. Gesamtgeb. d. Myk., 

8: 1 2- 1 8. 18S9. 
Geyler, H. Th. Exobasidium Lauri, nov. sp. Bot. Zeit. 32 : 321-326. pi. 6. 

1874. 
WoRONiN, M. Ueber die Sclerotienkranlcheit der Vaccinienbeeren. Mem. 

acad. imp. de St.-Pdtersbourg 36 (Ser. 7): 28-30. 1888. 

The members of this order are distinguished from other Basid- 
iomycetes chiefly in two characteristics, first, that the mycelium is 
strictly parasitic, producing generally a gall-like hypertrophy made 
up of mycelium and host tissue ; and second, that there is produced 
no definite sporophore; instead, the basidia break through the epi- 
dermis of the host. 

Four sporidia are commonly produced (occasionally five or six). 
The spores are curved, and germinate in nutrient media, so far as 
known, after one or more cross partitions are formed. Germina- 
tion is then more or less equivalent to a budding process, in which 
numerous spindle-shaped cells are produced. 

The genus Exobasidium is most important, and the majority of 
the species produce deformities upon different genera of heaths 
(Ericaceae). 

439 



440 



FUNGOUS DISEASES OF PLANTS 



II. (;all of heaths 

Exobasidiiiiii J 'accinii ( P ckl.) W'or. 

Richards, H. M. Notes on Cultures of Exobasidium Andromedae and of 
Exobasidium Vaccinii. Botan. Gaz. 21: ioi-io8. pi. 6. 1896. 

Shear, C. L. Cranberry Diseases. Bur. Plant Ind., U. S. Dept. Agl. Built. 
110: 35-37. //. 7. 1907- 

Relationship of forms. Much cross-inoculation work is needed 
to determine the relationship between forms of Exobasidium on 
different species of heath (Ericaceae). These fungi are found 

upon certain more or less 
closely related hosts, generally 
in bog-like habitats throughout 
considerable portions of Europe 
and North America. 

The fungus upon Vaccinium 
J'itis-idiEa is considered the 
typical form of the species 
here discussed. Upon the host 
referred to, pale rose or red- 
dish, thickened spots are pro- 
duced. The same species 
occurs, apparently, on other 
species of Vaccinium, also 
Gaylussacia and other genera, 
and it may be well briefly 
to refer to some of its related forms. No morphological char- 
acters of the fungus above mentioned have been found which 
would distinguish it from Exobasidium Oxycocci Rostr. on the 
cranberry {Vaccinium macrocarpon). On the cranberry, however, 
lateral buds are attacked, and as these exfoliate, a considerable 
portion of the shoot may become hypertrophied. The affected 
leaves are rose colored, and since they remain close together on 
the shoot, they are often called false blossoms. A form produc- 
ing characteristic galls on the young shoots of several species of 
rhododendron is generally regarded as distinct, and bears the 
name Exobasidium Azalea. Finally, there is an unusually large 
form described as Exobasidium Andromcdce Pk., which produces 




Fig. 215. Exobasidium Vaccinii on 
Rhododendron 



AUTOBASIDIOMYCETES 



441 



distortions on young shoots of Andromeda lii^nstrina. Galls of 
this latter form are hollow, bag-like structures which may attain a 
length of five or six inches. ' 

l-vichards employed the large form on Andromeda and Exo- 
basidiiim Jdccinii in some cross inoculations and was able to 
develop the leaf spot form of the gall on Andromeda from Exo- 
basidiinu Wxccinii, and also to produce this same form through 
spores from the galls on Andromeda. He also directs attention 
to the fact that the larger distortions in 
general are produced only during the 
early part of the year, that is, when the 
fungus attacks the young and sensitive 
tissue. Cross-inoculation work is at- 
tended with some difificulty on account 
of the diversity in season of the vari- 
ous forms, and probably also differ- 
ences in the susceptibility of the hosts 
as the season advances. 

The fungus. The hyphae are fine, 
much branched, and commonly inter- 
cellular. They are most abundant in 
the subepidermal layers, and in the case 
of the forms producing galls upon the 
young stems they are more or less con- 
fined to the cortical parenchyma. The 
basidia arise directly from the hyphae, 
pushing up between the epidermal cells. A basidium bears fre- 
quently four spores, but two to seven may be produced. The spores 
are elliptical or slightly curved and ordinarily measure 14-17 X 3/i. 
Among the basidia, at intervals, may appear certain branched 
conidiophores bearing small acicular conidia. This is apparently 
the chief conidial type in the genus Exobasidium. 




P"iG. 216. ExonAsiiuvM Vaccinii 
(After Woronin) 



III. HYMENOMYCETALES 



Among the higher Basidiomycetes the important forms from 
the view point of the economic plant pathologist are included in 
a few families of the Hymenomycetales. This order includes the 



442 



FUNGOUS DISEASES OF PLANTS 



great majority of the plants commonly known as mushrooms, toad- 
stools, punks, etc., plants exceedingly variable in size, form, and 
texture. The mycelium is generally abundant, and it is made up 
of relatively minute hyphse in loose wefts or flocculent masses, 
sometimes closely united into bands or strands (rhizomorphs), and 
often perennial. Sclerotia also occur. The fruit body varies from 
what is merely a close hyphal weft to bodies most diversely consti- 
tuted, and very complex in structure (sporophores). In fact, the fruit 
body may be felt-like, pellicular, leathery, fleshy, corky, or woody 
in texture. Conidial stages of several types are present in some 
families, but in this group these imperfect forms have not the same 
relative significance in propagation as in the Ascomycetes. The 
mycelium of a majority of the parasitic or wood-destroying species 
may be grown in artificial cultures in the laboratorj^ Frequently 
the best growth is obtained when such materials as dead wood, 
decayed leaves, and rich soil are substituted for the usual media. 

The families and genera here to be considered consist of solid 
sporophores, briefly characterized as follows : 

1 . Thclcphoraccce. The hymenial surface is more or less smooth. 
Sporophores are skin-like, gelatinous, or woody in texture, spread 
out over the surface of the substratum (resupinate), shelving, 
stalked, or considerably branched. Corticium and Stereum are 
important genera. 

2. Hyduaccce. The hymenial surface is usually spread over 
tooth-like divisions of the sporophore, the latter, however, some- 
times wart-like or even more or less briefly plate-like (lamelliform). 
The sporophores are very diversely formed. The genus Hydnum 
alone will be considered. 

3. Polyporaccce. The hymenial surface is generally spread over 
the inner surfaces of pores or narrow tubes, sometimes, however, 
over folds or shallow depressions between vein-like reticulations, 
occasionally more or less lamelloid. The sporophores are diverse, 
generally tough, often very large. Those most important in the 
production of tree diseases are typical pore-bearing species, which 
may be assigned to one of three closely related genera, — Fomes, 
Polyporus, and Trametes. 

4. AgayicacecB. The hymenial surface is confined to radial 
plates or lamellae, the latter, however, sometimes in the form of 



AUTOBASIDIOMYCETES 443 

folds or veins. The sporophores are generally fleshy, with a defi- 
nite cap, or pileus, usually provided with a central stalk, but also 
excentric, sessile, etc. Marasmius, Clitocybe, and Armillaria are 
some of the principal parasitic genera. 

Corticium, including resupinate species without setae (cystidia) 
on the hymenium. The spores are generally small, hyaline, and 
without appendages. 

Stereum is a diverse genus with broader characteristics. The 
sporophores are differentiated into several layers. They are only 
partially if at all resupinate, and often shelving, or even slightly 
stalked. 

Hydnum. The sporophores are provided with awl-like teeth 
arising from tuberculate, branched, or cap-like portions of the 
sporophore. No cystidia are present. 

Fomes, with sporophores generally bracket-like or hoof-shaped, 
sessile or stalked, and woody even when young. The pores are 
narrow, and the tissue between these is heterogeneous with the 
general tissue of the sporophore. 

Polyporus is similar to the preceding, except that the sporophore 
is at first fleshy, becoming harder, and it may be exceedingly diverse 
in form and size. 

Trametes. In this genus the species are generally of the texture 
of Fomes or Polyporus ; but the general tissue of the sporophore 
penetrates between the pores, so that there is homogeneity of 
substance. 

Marasmius is a genus of the relatively small gill-bearing fungi 
in which the plants become dry, yet, when remoistened, regain 
much their original forms. The cap is fleshy to leathery, the gills 
tough and distant, producing white spores, and the stipe cartilagi- 
nous or horny. 

Clitocybe, with more or less fleshy cap and stalk, the latter 
centrally placed, is characterized by decurrent gills (lamellae) and 
by the absence of any appendages, such as veil or volva. The 
spore powder is white and the spores hyaline. 

Armillaria. These forms are quite similar to the preceding ex- 
cept that when young the cap is attached to the stem by a veil, 
which upon breaking forms a more or less persistent ring (annulus) 
on the stem. 



444 



FUNGOUS DISEASES OF PLANTS 



IV. A ROOT AND STEM ROT FUNGUS 
Corticium vagum B. & C, var. Solani Burt. 

Atkinson, Geo. F. Some Diseases of Cotton. Ala. Agl. Exp. Sta. Built. 41 : 

30-39. 1892. 
Clinton, G. P. Rhizoctonia (Rosette). Conn. Agl. Exp. Sta. Rept. (1904): 

325-326. //. 26. Jigs. a-c. 
DUGGAR, B. M., and Stewart, F. C. The Sterile Fungus Rhizoctonia. 

Cornell University Agl. Exp. Sta. Built. 186: 50-76. Jigs. 15-2 j. 1901. 

Ibid. N. Y. (Geneva) Agl. Exp. Sta. Built. 186 : 4-30. Jigs. 13-23. 1901. 
Pammel, L. H. Preliminary Notes on a Root-Rot Disease of Sugar Beets. 

Iowa Agl. Exp. Sta. Built. 15: 243-251. pis. 3-4. 1891. 
Rolfs, F. M. Potato Failures. (Two Reports.) Colo. Agl. Exp. Sta. Bullts. 

70: 1-20. 1902; 91: 1-33. 1904. 
Rolfs, F. M. (Tomato Diseases) Corticiuin ".'agiiiniV^. & C). Fla. Agl. Exp. 

Sta. Rept. (1905): 46-47. 
SoRAUER. P. Pflanzenkrankheiten (2d ed.), /. <., 354-361. 

A fungus causing important diseases of the potato and perhaps 
of a large number of other herbaceous and even woody plants has 
recently been placed under the name above given. The various 




Fig. 217. Lettuce Seedlings attacked by Rhizoctonia 

plant diseases due to this fungus liad formerly ^been referred to 
the form genus Rhizoctonia, which is a genus established by 
De Candolle in 181 5, including certain sterile fungi occurring 
upon the roots of plants. There are great difficulties in determin- 
ing what might be considered species in forms which are re- 
ferred to this form genus, and the Corticium stage has not yet 



AirrOBASlDlOMYCETES 445 

been studied in sufficient detail to be of much assistance. Never- 
theless, there are certain characters of the mycelium by means of 
which it was believed to be possible more or less accurately to 
distinguish the Rhizoctonia from the mycelium of other fungi, or 
even with some accuracy to distinguish different species of Rhi- 
zoctonia, or sterile stages referred to the genus. It is only within 
the past four years that there has been found associated with the 
sterile mycelial form (the Rhizoctonia) this perfect stage, which 
has been determined as above given. It would seem probable, 
however, that we may look upon some of the rather diverse forms 
of Rhizoctonia as truly sterile stages of the Corticium mentioned. 

Historical. In Europe the genus Rhizoctonia received con- 
siderable attention by the early mycologists, and various forms 
were described at some length by the Tulasnes (185 1) and by 
Kiihn (1858). Moreover, all the general texts on plant diseases 
have given some consideration to these forms. In the United 
States the Corticijim vagiini of Berkeley and Curtis was un- 
known, apparently, prior to 1904 as the cause of plant diseases, 
yet the fungus had been described as No. 262 of the North 
American fungi, occurring upon the bark of pine in South 
Carolina. In 1891 Pammel, in some notes on beet diseases, 
described a beet root rot, which he believed to be due to Rhi- 
zoctonia Beta Kiihn. Yxovix the mycelial characters of the fun- 
gus this was unquestionably a Rhizoctonia. Further, in 1892 a 
sterile fungus as a cause of damping-off in cotton was reported 
from Alabama (Atkinson), and later the same author described 
damping-off of various seedlings by a similar unnamed fungus at 
Ithaca, N.Y. Since 1898 the various plant diseases due to this 
fungus have received considerable attention in this country. 
Work at the Cornell and New York (Duggar and Stewart), Ohio 
(Selby), Colorado (F. M. Rolfs), Florida (F. M. Rolfs), and other 
experiment stations has demonstrated that the various forms of 
this fungus are extremely important as the cause of various types 
of plant diseases in this countrv. 

Distribution and diversity of forms. The Rhizoctonia is un- 
questionably widely distributed in the United States and in Europe 
and Asia. In fact, wherever a careful study of plant diseases has 
been made, one or more forms of this fungus have been found. 



446 



FUNGOUS DISEASES OF PLANTS 



and it is very probable that some of the damping-off which has 
been ascribed to Pythium could be properly referred to damage by 
this fungus. It is not possible at the present time to say definitely 
that such damping-off diseases as those of cotton, lettuce, etc., are 
produced by the same species or race of Rhizoctonia as that which 

is found upon the potato, but 
there is reason to believe that 
the differences which occur 
between the various forms of 
the parasite upon a large num- 
ber of hosts are only such as 
might be considered varietal or 
racial, and in some instances 
we have unquestionably to do 
with physiological forms. It is 
certain, however, that Rliizoc- 
tonia Medicaginis De C. of 
Europe is a fungus very differ- 
ent from the common potato 
fungus of Europe and America 
and also from the common 
species producing damping-off 
of seedlings, rot of beets, etc., 
in this country. Moreover, a 
form which has been described 
(Duggar and Stewart) on rhu- 
barb is likewise a very different 
organism. It would not, how- 
ever, be surprising to find that 
a very large number of the 
other forms which have been 
discussed by various authors may be ascribed to one and the same 
species, the perfect stage of which would now appear to be Corti- 
cium vagnvi B. &C. var. Solani Burt. 

Effects upon the hosts. The fungus is perhaps most disastrous 
as a damping-off disease. The progress of the disease upon seed- 
lings resembles very closely that of Pythium, and it is affected by 
similar conditions. The plants that have thus far seemed to be 




Fig. 2i8. Rhizuctijma u.\ Radish 
(Photograph by H. H. Whetzel) 



AUTOBASIDIOMYCETES 



447 



most susceptible are such as lettuce (Fig. 217), sugar beet, celery, 
cotton, and the seedlings of various delicate, ornamental plants. 

Upon the potato the fungus has been known for more than 
half a century in Europe, but largely through the presence of a 
sclerotial stage upon the tubers. This typical sclerotial stage 




Fig. 219. Rhizoctonia on Potato: European (Upper) and 
American (Lower) Specimens 



has also been found abundantly in the United States during the 
past eight years, and it is unquestionably the same as the European 
form (Fig. 219). In this country, however, the Rhizoctonia was 
first found upon the stems of dying potato plants, and while it 
does not seem to be a very serious disease of potatoes, it is one 



448 



FUNGOUS DISEASES OF PLANTS 



of some consequence. It is perhaps not responsible for all the 
injuries which have been ascribed to it in Colorado, particularly 
in so far as the production of the disease known as " little potato" 




Fig. 220. Rhizoctonia producing a Crown Rot of Beets 

is concerned. The fungus, however, attacks the subterranean parts 
of the stem, as well as penetrating the roots, and the hyphas are 
found, for the most part, enveloping stem and root, or distributed 



I 



AUTOBASIDIOMYCETES 



449 



within the pith. The sclerotia, which are formed upon the surface 
of the potatoes, do not seem to produce, in any case, rotting of the 
tissues below. They are closely adherent, but merely superficial, and 
perhaps serve particularly for the distribution of the fungus. 

Upon the sugar beet this fungus produces, besides the damping- 
off already referred to, a characteristic form of rot. The leaves are 
affected at the bases, and these promptly wilt and decay. The fun- 
gus gains strength and penetrates into the superficial layers of the 
beet root, and frequently causes serious rotting, accompanied by 
cracking, as shown in Fig. 220. 

In Europe RJiizoctojiia Mcdicaginis has been found upon the 
beet, but that is a fungus very different from the Corticium, as 
subsequently mentioned. Moreover, RJiizoctonia Mcdicaginis has 
not been found in this country, although its hosts are such com- 
mon plants as the asparagus, alfalfa, and sugar beet. Some of the 
various hosts upon which the forms of the Rhizoctonia allied to 
Corticium vagitni var. Solani have thus far been found in America 
are as follows : 

Sugar beet, Beta vulgaris^ 

Bean, Pliaseoliis vulgaris, 

Carrot, Daucus Carofa, 

Cabbage and Cauliflower, Brassica o/eracea, 

Cotton, Gossypiuiii hirsutum. 

Lettuce, Lactuca sativa, 

Potato, Solan II in tuberosum, 

Radish, Raphanus sativus, 

Sweet potato, Ipomcea Batatas, 

Pumpkin, Cucurbita Pepo, 

Watermelon, Citrullus vulgaris, 

Garden pea, Pisuin saiivuin, etc., 

as well as upon many species of ornamental plants and weeds. 

Upon the tomato plant this fungus attacks also the subterranean 
parts of the stem and may be of importance where the soil is poorly 
aerated. It may also occur upon the fruits when these are in con- 
tact with the soil, but it is not probable that it becomes a fruit 
disease except when fruit has been previously injured in some 
manner. Upon either the potato or the tomato the fruiting stage 
may develop upon the stems above the surface of the ground to 
a distance of several inches. 



450 



FUNGOUS DISEASES OF PLANTS 



Characters of the fungus. The mycelium varies considerably 
in form, depending upon age, or the conditions under which grown. 
In diseased tissues where there is abundance of water, or in 
pure culture, the young hyphae develop branches, which are usually 
inclined at an acute angle to the direction of growth of the 

parent branch, although subse- 
quently the two may grow par- 
allel. The branch is usually 
somewhat narrowed or con- 
stricted where united with the 
main hypha, and a septum is 
formed at a distance of several 
micromillimeters from the 
point of origin of the branch. 
The hyphae may be almost 
hyaline when young, but very 
generally become yellowish 
brown with age. Furthermore, 
in age the branches appear to 
be more at right angles, at 
least, so far as the origin is 
concerned. Upon many host 
plants, and especially when the 
fungus is grown in pure cul- 
tures, a short tufted growth of 
the mycelium may occur. The 
hyphae of these tufts are brown, 
closely septate, constricted at 
the septa, and often branched 
in an irregular dichotomous 
fashion (Fig. 222, /;). In the 
latter case the hyphae readily 
break up into short hyphal lengths, consisting of a single cell or 
more, and these cells are able to germinate within a few hours 
when placed in fresh nutrient media. Germination is commonly 
by means of a germ tube protruded from a septum. A germ tube 
may even, in some cases, pass through a neighboring cell. It would 
appear that the fruiting stage usually develops upon living plants. 




I-'k;. 22\. RlllZoCTliNIA ()\ 1>K.\N 

Stems and Puds. (Photograph by 
H. H. Whetzel) 



AUTOBASIDIOMYCETES 



451 



In the case of the potato, it forms a membranous layer inclos- 
ing the stem for several inches above the surface of the ground. 
This layer is composed of rather loosely interwoven hyphae, and 
on account of this character it is difficult to say if the plant is 
properly placed under the genus Corticium, or whether it might 
not with equal propriety be considered a species of Hypochnus. 
The basidia are short, cylindrical, or oblong, and apparently many 




Vic. 222. CORTICIVM VAGUM ^■AK. SoLANI 
a, young hyphje ; /', cells from growth in tufts ; f, basidia and spores 

may be produced from a single parent hypha, each basidium being 
cut off from the hypha by a septum placed in the manner charac- 
teristic of the branching mycelium. The basidia bear four sterig- 
mata and spores, although commonly only two may be observed 
at one time. The spores, according to Rolfs, are somewhat ellip- 
tical or irregular in outline, frequently obovate and nearly hyaline, 
9-15 X 6-1 3 /x. Spore germination proceeds in ordinary nutri- 
ent media, and as a rule a septum is formed in the germ tube 
shortly after it emerges from the spore, the proximal portion of 
the germ tube being somewhat less in diameter. When produced 



452 



FUNGOUS DISEASES OF PLANTS 



upon the majority of hosts the Corticium stage disappears by the 
time the host plant is dead. 

A considerable amount of study is demanded in order that it may 
be determined what may properly be considered species or varieties 
within this group of plants. Cross-inoculation work is particularly 
important, yet it is also difficult, on account of the following fact : 
After being grown in culture for some time the fungus seems to 
change to a certain degree, at least, its relation to the host as a 
parasite, and it is possible that direct transference of the fungus 
from one host to another would not yield the same results as by 
the use of old cultures or cultures grown upon diverse media. 

This fungus in all of its forms is readily culturable upon the 
ordinary nutrient media, such as bean stems, potato and beet cylin- 
ders, agars, corn meal, etc. It is, moreover, not difficult to make 
dilution cultures, even though the fungus usually grows upon those 
parts of the plant where bacteria would normally be present in 
abundance, as upon roots and underground stems. By carefully 
washing the mycelium in distilled water and then by the use of 
acidulated media, as suggested under cultural methods, the fungus 
may be readily separated from contaminating bacteria. 

Control. No effective preventive measures for the forms of this 
fungus have yet been found. It would appear, however, that gen- 
eral sanitary precautions are important. Good drainage in the 
upper layer of the soil and the presence of a layer of sand, charcoal, 
or cinders serve in great measure to prevent the appearance of 
the fungus. An aerated soil is also less liable to be seriously 
affected, owing, perhaps, to the better health of the roots than one 
which is poorly aerated. The application of lime and other fungi- 
cidal mixtures to a soil is commonly useless. This fungus is 
apparently not readily affected either by weak alkalis or acids ; but 
since acid conditions render the host more susceptible, liming has 
value. 

V. HEART ROT OF SUGAR MAPLE 
Hydnum septentfionale Fr. 
Atkinson, Geo. F. Geological Survey of La. (1889): 335-336. pi. 3S. 

Among the numerous species of the genus Hydnum, which 
embrace the commoner toothed Basidiomycetes, it would seem 



I 



AUTOBASIDIOMYCETES 



453 



that few may be classed as true parasites, the majority growing 
upon logs, stumps, etc., after death, or after being felled. Some, 
however, are unquestionably in part parasitic to the extent that 
they may be considered disease-producing in woody plants. 

This species occurs extensively in the United States, principally 
on the sugar maple {Acer saccharuni), but also on other species 
of deciduous trees. It is likewise found generally distributed in 
Europe, The effects of this fungus upon the wood of diseased 
trees has not been carefully studied, but there is certainly a heart 
decay, probably more or less in the manner of some of the diseases 
subsequently described. 

The sporophores appear in bracket-like clusters, which may be 
20-30 cm. wide and 50-80 cm. or more in longitudinal extent. 
The general color is creamy white, and the texture at first fleshy, 
becoming more fibrous. The pileus, often 3 cm. thick, presents an 
almost plain upper surface, slightly scaly, all of the pilei being 
united posteriorly. Teeth slender and often 12 mm. long. This 
is one of the largest fungi in this genus, and it is striking in 
appearance. 

A number of species of this genus, or species of closely related 
genera, particularly the resupinate forms, are found upon dead and 
decaying wood. More beautiful and structurally differentiated of 
the Hydnaceae, such as Hydiutui erinaccus, Hydnnni coralloides, 
etc., are also found upon dead logs and trees and sometimes even 
upon decayed portions of living trees. 

VI. WHITE ROT OF DECIDUOUS TREES 

Polyporus sqitamosiis (Huds.) Fr. 

BuLLER, A. H. R. The Biology of Polyporus squamosus Huds.. a Timber- 
destroying Fungus. Journ. of Economic Biology 1 : 101-138. pis. ^-g. 
1906. 

The great scaly Polyporus, sometimes known as the Saddle-back 
fungus, is a tree-destroying parasite whose conspicuous bracket 
sporophores are in many regions well known upon ornamental, 
shade, and forest trees. The fungus occurs throughout a large por- 
tion of Europe, but it has been found as yet only sparingly, it 
would seem, in the northern portion of the United States. The 



454 



FUNGOUS DISEASES OF PLANTS 



distribution of this fungus, however, is doubtless much more ex- 
tensive, although the indications are that it is uncommon in regions 
which are rather dry throughout the summer. 

The sporophores of this fungus have been reported upon various 
species of maple (Acer), oak (Quercus), elm (Ulmus), basswood 
(Tilia), willow (Salix), ash (Fraxinus), etc.; therefore it may be ex- 
pected upon practically any of the deciduous trees. There seems 
to be no record of its occurrence upon conifers. The tree attacked 




Fk;. 223. PoLVPORus sQu.iMosus, Lower Surface. (After ]>uller) 

by this fungus dies gradually, and the effect may in general be 
called a white rot, since there is no marked discoloration, and the 
presence of the mycelium is to lighten rather than darken the 
effect. The hyphae probably obtain entrance through wounds, as is 
the case with most other related fungi. The mycelium then grows 
upward and downward, first in the central portion of the tree, 
apparently having little power to affect directly the living portions. 
It gradually works and spreads outward, killing the young wood 
doubtless prior to invasion, and finally breaking through the sur- 
face and producing sporophores after a period of years. 



AUTOBASIDIOMYCETES 



455 



The hyphas arc h}alinc, considerably septate, and often show 
clamp connections when growing in the vessels. They grow more ' 
quickly in the vessels, but are not ultimately assembled into strands 
in these parts. The wood is eventually separated into plates or 
cuboidal areas, and the texture of the wood becomes light and corky. 
The separation of the wood into plates is accomplished by the 
growth of white strands or bands of the mycelium in all three direc- 
tions, that is, radially, tangentially, and longitudinally. The wood 
elements, which gradually disappear under the solvent action of 




Fig. 224. PoLi-poRcs sqcimosus. Upper Surface 

the fungus, are largely those which are less lignified, such as the 
fibers between the vessels, that is, those usually produced only dur- 
ing spring growth. In the dissolution of the cells, first the contents, 
next the secondary cellulose layer, and finally the middle lamellae 
disappear, so that during the process the cells do not become sepa- 
rated in the early stages of decay. 

The mycelium unquestionably possesses a variety of enzymes. 
According to Buller, " from an enzymotic study of wood undergoing 
decay from the agency of Polyponis squaviosus evidence was taken 
that various enzymes are excreted by the fungus mycelium. Thus 



456 



FUNGOUS DISEASES OF PLANTS 



the disappearance of starch, proteids, and cellulose suggests that 
the fungus produces amylolytic, proteolytic, and cyteolytic enzymes." 
A direct study of this point was attempted by making extractions 
from fresh, young fruit bodies, and testing these. While this may 

not be an absolute criterion for 
the basis of an opinion as to the 
enzymes produced in the my- 
celium, it is nevertheless inter- 
esting that laccase, tyrosinase, 
amylase, emulsin, protease, 
lipase, rennetase, and coagu- 
lase were seemingly present, 
whereas negative results were 
obtained in the tests for pec- 
tase, maltase, invertase, treha- 
lase, and cytase. However, a 
study of the destruction of wood 
by the fungus furnishes evidence 
that the mycelium produces cy- 
tase and possibly hadromase." 

The sporophores arise singly 
or in clusters of a few brackets, 
usually during summer and early 
autumn. It requires but a brief 
period for these sporophores to 
attain their growth, brackets 
measuring 15-25 cm. in width 
having been observed to com- 
plete growth within two weeks. 
The mature sporophore is yel- 
lowish brown above, and the 
surface of the cap is thrown 
into characteristic brown scales. 
The plants are commonly i 5-30 cm. broad, although one speci- 
men measuring 65 cm. and weighing approximately six and a half 
pounds has been found (Buller). The margins of the pileus are 
slightly revolute even on maturity, the lower surface of the pileus 
yellowish, with pores at first small, later expanding, and angular. 




Fig. 225. PoLvi'ORUs squamosus: Pro- 
gressive Destruction of Wood 
(After Buller) 



AUTOBASIDIOMYCETES 457 

The flesh is white and soft when youn<jj, becoming tough with age. 
Nevertheless, this sporophore persists but a single season, while a 
diseased tree may continue to jDroduce si:)()rophores throughout a 
period of years, and even for some time after having been felled. 

In the development of the sporophore a knob-shaped, fleshy body 
appears, from which may arise one or more short stems, and the 
changes in one of the latter are usually about as follows : An apical 
depression is the first evidence of the pileus. Further growth in 
the stem is hyponastic, raising the depression toward the horizontal, 
and at the same time there is rapid and distinctly one-sided lateral 
expansion, and later, thickening in the region of the depression, 
so that it becomes a definite pileus, with the greatest growth on the 
sides farthest from the axis of attachment, thus eventually giving 
the excentric or almost lateral type of sporophore. 

The hymenium is very early differentiated, first as very shallow 
reticulations, but a downward growth of the netted ridges develops 
in time the relatively deep pores of the mature sporophore (Fig. 223). 
The basidia and spores are not unusual in form. The latter measure 
about 1 2 X 5 /x. It is not without interest to note that the spores 
are forcibly thrown from the sterigmata in this species, and doubt- 
less in practically all other species of Basidiomycetes, the form of 
the sterigmata and the attachment of the spores to these frequently 
suggesting the possibility of well-regulated tensions. By a com- 
paratively accurate method Buller estimated the number of spores 
produced in a single pore, and found it to be about one million, 
seven hundred thousand. The spores, like those of mold fungi, 
will withstand immersion in water for a long period. 

VII. DECAY, OR BROWN ROT, OF TREES 
Polyponis snlpJiureiis (PjuII.) Fr. 

Atkinson, Geo. F. Studies of Some Shade Tree and Timber Destroying 
Fungi. Cornell Agl. Exp. Sta. Built. 193: 20S-214. 1901. 

ScHRENK, H. VON. Polyporus sulfureus (Bull.) Fr. Div. Veg. Phys. and Path., 
U. S. Dept. Agl. 25: 40-52. ph. 11 (in part), ij. 1900. 

The sporophores of no other fungus present, probably, a more 
striking appearance than the fresh, vigorous, sulfur-yellow cluster 
of the above species. It cannot be considered a very vimlent 
disease-producing organism, in spite of its wide distribution and 



458 



FUNGOUS DISEASES OF PLANTS 



the variety of host plants upon which it is reported. This fungus 
has been found practically throughout the world where trees grow. 
It is unquestionably more abundant in humid climates, yet minor 
or nonpersistent, unfavorable conditions do not readily affect it. 

This Polyporus is of special interest because of its occurrence 
upon a large variety of trees. Deciduous trees are more commonly 
attacked, yet both in TLurope and America it is not infrequently 
found upon conifers. It is perhaps oftener noticed upon such 




Fig. 226. Por.vpoRL-s sclphckkus ox Exposed Roots of a Living Tree 
(Photograph by L. 11. Childers) 

forest and shade trees as oak, walnut, butternut, ash, black locust, 
poplar, and willow. Among orchard trees the cherry in old orchards 
is a comnKjn host, but pear and apj^le trees are also susceptible. 
Moreover, the sporophores of this fungus may appear upon fallen 
trunks and stumps, and it appears to be true that the mycelium of 
the fungus may develop extensively in fallen trunks. 

The coniferous trees upon which it has been more frequently 
observed are the larch in Europe and the hemlock and spruce in 
America. 



AUTORASIDIOMYCETES 



459 



The mycelium evidently establishes itself in a saprophytic man- 
ner upon dead branches or in the decayed wood about knot holes, 
thence gaining entrance to the heartwood of the main trunk. 
After growing for years in the latter, it may develop sporophores 




Fig. 227. PoLYPORus sulphureus on White Oak, showing Nature of 
Decay. (Photograph by Geo. F. Atkinson) 

where wounds occur, permitting the vigorous mycelium to reach 
the surface readily. In other cases the path of the mycelium of this 
fungus evidently extends directly to the surface, killing the wood 
as it progresses. Sporophores may then be developed on the 
otherwise uninjured bark surface. In general, the growth of the 
mycelium causes a prompt decay of the wood, the latter becoming 



460 FUNGOUS DISEASES OF PLANTS 

brown and, to a considerable extent, separated into plate-like areas, 
corresponding in their radial diameters to the seasonal wood rings. 
These plates are subsequently broken into smaller areas by lateral 
contact, and in all of the clefts thus formed by the processes indi- 
cated, the mycelium often grows (especially in deciduous trees) in 
sheath-like strata, the particular appearance of the mycelium, how- 
ever, being modified in different hosts, largely depending upon the 
density of the wood (Fig. 227). In all cases the wood is brittle in 
the last stages of decay and may be readily reduced to a powder. 

According to von Schrenk the detailed changes induced in the 
wood of the spRice may be stated as follows : 

Minute changes in the wood.^ The minute changes which the mycelium of 
Polyporus siilfiireiis induces in the wood cells are such that they cannot be 
mistaken. It has been mentioned that the annual rings break into bands which 
curve inward as the process of drying goes on. A tangential view of several 
of these bands before they have broken will present an appearance such as is 
shown on PI. XI, fig. 4. A large number of fissures have formed both across 
the wood fibers and parallel with them. The latter are more prominent — the 
cross fissures never occurring alone, but generally connecting several longi- 
tudinal fissures. It will be noted that the breaks are characterized by sharp 
right angles, and in many places a stepladder arrangement is evident. In the 
early stages of attack the wood fibers turn red-brown and shrink. As a result, 
fissures are formed in the walls of the tracheids, which extend diagonally across 
the wall at an angle of approximately 45 degrees. (PI. XI, fig. i). The med- 
ullary ray cells are at this point still intact, and hold together the more or less 
brittle wood fibers. The next stage in the decomposition consists in the ab- 
sorption of the medullary rays. This allows the wood fibers to contract more 
than up to that time, and as a result breaks occur. These breaks form at first 
so as to connect adjacent cavities left by the absorption of the medullary rays. 
The wood fibers tend to curve in one direction or another and break at the 
weakest point, namely, between two cavities, where the opportunity for curva- 
ture is greatest. What determines the direction of curvature of the wood fibers 
has not yet been explained. In the illustration the curvature is toward the 
right. This curving has the effect of bringing medullary rays which are in 
different longitudinal rows approximately into a line. Thus at " a " two cavi- 
ties are shown which are separated by a curved fiber which sooner or later will 
break, uniting the two. At first two ray cavities are joined, then more, until 
long longitudinal holes are formed, such as are shown in fig. 4 of PI. .XI. The 
reason for the sharp edges is now very apparent, likewise why these fissure fig- 
ures appear only on a tangential view, while on the radial view one simply sees 
the fissures as lines extending at right angles acr6ss a ring of wood (PI. XIII). 

^ The plates referred to are also those of von .Schrenk's bulletin. 



AUTOBASI I )I()M VCETES 46 1 

On the oak and other cleeiduous trees the mycehum is much 
more dense than in the spruce, for example. In the latter the 
mycelium is said to be colorless. It is, however, in some instances, 
slightly cream colored when approaching the surface. Hartig 
has mentioned the appearance of a secondary fruit form in the 
oak. This also occurs upon other hosts, and cultures from frag- 
ments of the sporophore have promptly given, on various culture 
media, a vigorous cream colored mycelium, which with age becomes 
mealy in appearance, due to the extensive formation of conidia, 
such as are referred to above. These conidia correspond to those 
which are considered by Brefeld to be the typical oidial stage 
frequently present in Hymenomycetes. 

The sporophores of this species appear usually during the late 
summer or early autumn, in large, shelving clusters (Fig. 226) or 
sometimes scattered. The form of the pileus may be considerably 
modified by its position upon the host and by its relation to other 
sporophores. The sporophore is fleshy and of a cheese-like con- 
sistency when young, becoming harder and woodier with age. At 
first the entire sporophore is yellow, but later the under, pore-bearing 
surfaces are bright yellow, while the upper surfaces are ordinarily 
orange-red. The flesh is at first white, becoming slightly cream 
colored with age. These sporophores may grow in such masses 
as to attain a length and height of from 30 to 40 cm. The in- 
dividual pilei may be entirely sessile or slightly stalked, and loosely 
scattered or so closely massed as to be united in the vicinity of the 
host. The young plants have a distinct odor, which becomes pro- 
nounced with age. The pores are found on the under surface 
only. They are about 4 mm. deep, with nearly circular outlines. 
The spores are hyaline, ovoidal in outline, and usually measure 
7-8 X4-5/i. 

Control. In controlling this fungus the only practical measures 
are to cover up as promptly as possible with tar or other antiseptic 
materials all wounds, either natural or as a result of pruning, and 
further, to destroy all sporophores as they appear. The spores de- 
velop very quickly after the sporophores are mature, and it is very 
probable that their distribution is effected by means of insects, 
which may be attracted by droplets of a sugary substance which 
may accumulate on the under surfaces of the sporophores. 



462 



FUNGOUS DISEASES OF PLANTS 



VIII. POLYPORUS: OTHER SPECIES 

In addition to the species described at length, the following 
may be mentioned also as among those of special importance, 




« 



Fig. 228. PoLYPORVS bore.il/s ox T,iving Tsuga. (Photograph by 
Geo. F. Atkinson) 

occurring in Europe and in America, which have received more 
or less recent consideration from the standpoint of shade and 
forest tree diseases. 



AUTOBASIDIOMYCETES 



463 



Polyporus borealis (Wahl.) Fr. is a characteristic and destructive 
disease of the spruce in Europe, and it occurs on a variety of conifers 
in America.^ The bracketed sporophores are clustered, as shown 
in Fig. 228. They are fleshy for some time, but finafly tough and 
dry. The spores are minute, measuring 4-5 x 3 ix. The myceUum 
de\'elops abundantly in the wood with typical markings (Fig. 229). 




Fig. 229. FoDTOKi's iioR/-:.ujs: Longitudinal Section ok Log, 
SHOWING Mycelium. (Photograph by Geo. F. Atkinson) 

Polyporus carneus Nees causes a red rot, or peckiness, in the 
common red cedar {Junipcms virginiana) and in the southern red 
cedar {Jnnipcriis barbadcjisis), as well as in other conifers.'-^ 

Polyporus Juniperinus von Schrenk is apparently the cause of 
the white rot of the red cedar.^ 

Polyporus Schweinitzii I^^-. is abundant in Europe on the Scotch 
pine, Weymouth pine, and the larch.^ This species is )-ellowish 

1 Atkinson, Geo. F. Cornell Agl. Exp. Sta. Built. 193: 202-20S. 1901. 

2 Schrenk, H. von. Div. Veg. Phys. and Path., U. S. Dept. Agl. Built. 21 : 1-22. 
ph. i-'j. 1900. 

3 Schrenk, H. von. Div. Veg. Phys. and Path., U. S. Dept. Agl. Built. 25 : 18-24. 



464 



FUNGOUS DISEASES OF PLANTS 



white, with httle or no stipe, yellowish green pores, and spores 
7-8 X 3^/x. 

Polyporus Betulinus (Bull.) Fr. is the cause of a sapwood decay 
in several species of birch, and it is very widely distributed. 

Polyporus Fraxinophilus Pk., a rather small white form with 
pileus 5-10 X 2.5-4 cm., produces an important disease in the 
white ash {Fraximts americand)} 



IX. FOMES 

Atkixson, Geo. F. Studies of Some Shade Tree and Timber Destroying 
Fungi. Cornell Agl. Exp. Sta. Built. 193 : 199-235. yfc'-j. 5 d-9^. 1901. 

SCHRENK, H. VON. Diseases of Deciduous Forest Trees. Bur. Plant Ind., 
U. S. Dept. Agl. Built. 149 : 1-85. ph. i-io. 1909. 

The genus Fomes includes 
among its representatives the 
most destructive forest-tree 
organisms in this order of 
fungi. The conspicuous 
bracket-like and hoof-shaped 
sporophores are familiar to 
all who have given the typ- 
ical, temperate moist forests 
any attention. They are, for 
the most part, moisture- 
loving, wound fungi ; and, 
consequently, they find in the 
conditions of the forest the 
opportunity for their ma.xi- 
mum destructiveness. They 
may be entirely absent from 
shade and meadow trees. 
Among many species of com- 
mon occurrence, special 
mention should be made of 
Fames igiiiariiis, Fomes 

Fig. 230. FoMHs FomiNTAKws on Ue.vu fomeiitarius, and Fomes Pi- 
Beech. (Photograph by Geo. F. Atkinson) nicohx. Fomes applauatus is 




1 Schrenk, II. von. Bur. I'lant Ind., U. S. Dept. Agl. Built. 32 : 1-18. pis. i-j. 1903. 



AUTOBASIDIOMYCETES 



465 




Fig. 231. FoMKS Pinicola on Dead Hemlcjck. (Photograph by 
Geo. F. Atkinson) 



also a conspicuous form. Under the conditions now necessarily 
confronting those interested in forestry, there is no practical method 
of control. In the woodlot these fungi will prove far less serious. 
Fomes igniarius (L.) Gillett. This species, commonly known as 
the false tinder fungus, occurs upon a great variety of deciduous 



466 



FUNGOUS DISEASES OF PLANTS 



^ 




IMC 



232. FoMi-s .ipp/.AX.iTcs o^ Hard AIai'I.k: Smam. Si'F.riME.Ns 
(Photograph by Geo. F. Atkinson) 



trees. In the moist forest it is often difficult to find a beech 
tree {Fagiis grandifolia) ten inches or more in diameter which is 
not seriously affected. The fungus is also destructive to hard 
maple {Acer saccJiariini), yellow birch {Bctnla lutea), aspen {Popii- 
lus t remit hides), and certain oaks {Qticrciis spp.) in their ranges. 



AUTOBASIDIOMYCETES 467 

The sporophore varies in form from the shape of a hoof to that 
of a thick bracket. The upper surface is, with age, black, indurated, 
and cracked, also showing concentric ridges ; while the lower sur- 
face is commonly, during the growing season, cinnamon-brown. 
The mycelium grows within the heartwood, which is generally 
converted to a soft mass, bordered by black rings. 

Fomes fomentarius (L.) Fr. This fungus occurs in situations 
similar to those mentioned for the preceding organism. It is far 
more common upon beech, yellow birch, and hard maple. The 
sporophores may be found upon living trees, but they are produced 
in far greater abundance after the death of the tree affected. They are 
distinctly hoof-shaped (Fig. 230), with a grayish upper surface and a 
lower surface which is light brown or gray-brown during the summer. 

Fomes Pinicola Fr. In the moist temperate regions this fungus 
induces a decay in a variety of conifers, especially pines {Pimts spp.), 
spruces {Picea spp.), and balsam {Abies balsamca). The sporo- 
phore is a broad, relatively thick bracket, with a creamy white 
under surface. The upper surface is dark, generally with broad 
ridges, the lower of which may be reddish to bright red-brown 
in color (Fig. 231). The sporophores generally develop after the 
death of the tree. 

Fomes applanatus (Pers.) Wallr. The sporophores of this fun- 
gus constitute the most conspicuous forest brackets. The fungus 
occurs upon a variety of deciduous trees, but it is regarded as more 
commonly saprophytic. In any event, it is important in the decay 
of trees injured by fire or water, and of fallen trunks. 

X. A BROWN ROT OF CONIFERS 

Tmmetcs Pi/ii (Brot.) Fr. 

Hartig, R. Trametes Pini Fr. Wichtige Krankheiten der Waldbaume. 
pp. 43-61. //.J. yf^j-. 7-/9. 1874. 

Among the various species assigned to the genus Trametes 
there are some important wood-destroying fungi. Trametes Pini 
is common in the United States throughout the coniferous forests. 
In the Ozark pine forests of Missouri it is the chief cause of loss 
among fungi. In some regions which have been cut over there 
have been left thick forest groves, and these often consist very 



468 f^UNGOUS DISEASES OF PLANTS 

largely of trees that are affected by this " punk." The fungus is 
also common in pine forests of northern Europe, occurring there, 
as well as in parts of America, on the spruce. According to 
Hartig, trees are more subject to this fungus in woods exposed to 
strong winds, since the breaking of limbs of older trees by any 
cause invites infection. 

The phenomenon of infection and the spread of the fungus 
within the tree are doubtless accomplished in a manner similar to 
the cases already described. The wood pervaded by the fungus 
assumes from the first a deep red-brown color. There is no 
checking, in the proper sense, although occasionally the annular 
rings may in one or more regions be readily separable. The chief 
characteristic, however, so far as the effect upon the wood is con- 
cerned, is to be found in the development of bleached pits or 
pockets. The formation of these may be readily understood when 
it is ascertained that the action of the mycelium is first to delignify 
the cells, then to dissolve the middle lamellae, so that the cells are 
set free prior to general dissolution. The wood is therefore in 
certain areas transformed to more or less pure cellulose and con- 
sequently bleached in appearance. The pockets appear more or 
less circular in cross section, and vary in shape from ovoidal to 
long-cylindrical. The pockets are at first to be found chiefly in the 
spring wood portion of the annular ring. The mycelium is yel- 
lowish in color and is not massed in strands in the pockets. 

In the pine the sporophore is almost invariably formed in a 
wounded area, and the fruit body may be in the form of an in- 
crusted, brown-black stratum, or as a hoof-shaped bracket. These 
sporophores are perennial, and for a few years the annular layers 
which are developed successively upon the fruiting surfaces in- 
crease the size of the fruit body. Subsequently, however, there 
may be no increase in size from the deposition of new layers, or 
the strata may be of smaller extent, in case of the death of a por- 
tion of the last-formed annular layer. The fruit body may attain 
a considerable age, and each year or season of growth will be out- 
lined by a somewhat prominent concentric ring, or surface ridge. 
The lower or marginal ridge, including the hymenial surface, is of 
a light brown color, but older ridges become black and very irregular 
in outline. A section of a sporophore shows a layered structure, 



AUTOBASIDIOMYCETES 469 

corresponding to the surface rings. The new growth apparently 
takes place from all exposed surfaces which are still corky in tex- 
ture, including the lower margins of the sporophores. Doubtless 
the sterile basidia continue their growth as vegetative hyphae. The 
sporophores may be produced high upon the trunks, and since an 
annual crop of spores is produced, they are most favorably situated 
to be blown upon other trees. Young conifers are in part protected 
from infection by the resinous exudates which form over wounds. 
Control. No method of controlling this fungus is possible, ex- 
cept by preventing, as far as may be, the causes leading to the 
breaking of living branches. In well-cared-for forests it is practi- 
cable to fell diseased trees as promptly as possible or to destroy 
developing sporophores. 

XI. ROOT DISEASE OF SUGAR CANE 
Marasmius plicatus Wakker. 

Cobb, N. A. Fungus Maladies of the Sugar Cane. Hawaiian Sugar Planters' 

Exp. Sta., Div. Path, and Phys. Built. 6 : iio pp. (of. 24-26, 50). 1906. 
Fulton, H. R. The Root Disease of Sugar Cane. La. Agl. Exp. Sta. Built. 

100: 1-21. figs. 1-8. 1908. 
Howard, A. On Some Diseases of the Sugar Cane in the West Indies. 

Ann. Bot. 17: 373-411. pi. 18. 1903. 
Wakker, J. H. Eine Zuckerrohrkrankheit, verursacht durch Marasmius Sac- 

chari n. sp. Centrbl. f. Bakt., Par. und Infektionskr. 2 (Abt. 2): 44-56. 

fig^- 1-5- 1896. 

A root disease of the sugar cane in Java was first described by 
Wakker, and the causal fungus was given as Marasmius Sacchari. 
A similar disease was subsequently found in other portions of the 
West Indies, in the Hawaiian Islands, and recently in Louisiana. 
It is now known to be widely distributed in the southern United 
States. From the work which has been done thus far it seems 
apparent that several species of Marasmius may be concerned in 
the production of a more or less common type of root disease. In 
all cases the fungus appears to be merely a weak parasite, and it 
frequently gains entrance to the host through the wounds upon 
cuttings and seed plants. 

Symptoms. Stools of the sugar cane affected by this fungus 
are commonly smaller and poorly rooted, so that the disease be- 
comes especially evident during conditions of drought. 



470 



FUNGOUS DISEASES OF PLANTS 



Having gained entrance through the stubble or plant canes the 
fungus invests the root system, and also the lower joints of the 
stem, cementing the leaf sheaths together near the base with a 
whitish mycelium. Not only is great injury done to the growing 
stools, but a vastly greater loss results from missing hills of cane, 
on account of the fact that the diseased stubble, or plant canes, 

may be so covered up by the 
fungus that few stalks will be 
produced. 

The fungus. Under favor- 
able conditions (constant mois- 
ture being indispensable), the 
mycelium which is constantly 
associated with the root dis- 
ease may develop fmit bodies, 
or sporophores. The type of 
sporophore in the case of the 
Louisiana disease is shown in 
Fig- 233. It is described by 
Fulton as follows : 

The pileus is dirty white, becom- 
ing somewhat darker with age ; it is 
usually about three fourths of an inch 
in diameter, but may attain a size of 
an inch and one fourth. When 
young it is convex, and at maturity 
is almost flat or perhaps slightly con- 
cave. Its surface is smooth. On 
the under side are the radiating gills 
which have an even, thin edge, and 
a straight, radial direction. The long 
gills extend from the margin to the stem, and are attached to the stalk itself 
rather than to a prominent ring about the stalk. Other shorter gills extend 
from the margin just far enough to fill in the angles between the longer gills. 
The stipe is about equal in length to the diameter of the cap, or in some cases 
somewhat less. It usually arises from the side of the leaf sheath, and is some- 
what curved so as to bring the cap into a horizontal position. It is normally 
attached to the cap at its central point, but at times this attachment is some- 
what eccentric. The stipe is smooth externally, except at the base, which is 
downy and also enlarged. The whole fruit cap persists for about a day, and then 
gradually dries, losing its form, but not undergoing immediate disintegration. 




Fig. 233. Marasmius plicatus on 

Sugar Cane. (Photograph by 

H. R. Fulton) 



AUTOBASIDIOMYCETES 471 

The spores, white in mass, are hyaline, ovate, averaging 6-8 x 
5-6 ft, with a prolongation at the base. The fungus has been 
grown in pure cultures, and inoculation experiments from such 
pure cultures have yielded the typical disease, this in turn show- 
ing the characteristic mycelium. The mycelium in culture makes 
the best growth at from 25° to 30° C. The fungus spreads rapidly 
by means of the vigorous mycelium, and the sporophores are pro- 
duced so infrequently that spores would seem to play a minor part 
in the distribution of the species. 

Control. As a result of his studies, Fulton cites the following 
conditions as favoring the growth of the organism. 

1 . Slowness of germination and early growth of the canes. 

2. Improper cultural procedures. 

3. Unsuitable soil. 

4. Bad drainage. 

5. Unfavorable seasonal conditions. 

6. A stubble crop. 

These facts make it evident that prevention should be concerned 
with general methods of sanitation, such as the destruction of all 
infected waste material, the rotation of crops, selection and disin- 
fection of seed cane, and also the planting of the more resistant 
varieties. 

XII. ROOT ROT OF FRUIT TREES 
Clitocybe parasitica Wilcox 

Wilcox, E. M. A Rhizomorphic Root-Rot of Fruit Trees. Okla. Agl. Exp. 
Sta. Built. 49: 1-32. pis. i-ii. 1901. 

For some years attention has been called to a destructive disease 
of apple trees in Missouri, Oklahoma, and adjacent states, character- 
ized primarily by the death of the root system. There is commonly 
associated with this disease an invasion of the root system by the 
mycelium of some one of the mushrooms. Wilcox has concluded 
that the disease in Oklahoma is caused by a fungus described as 
a new species, Clitocybe parasitica. He has found this fungus 
constantly associated with the root rot of the apple, and also with 
a similar disease of peach and cherry, as well as of certain native 
species of oak. Other observers have apparently not been able 
to conclude that a Clitocybe is the cause of the disease prevalent 



472 



FUNGOUS DISEASES OF PLANTS 



throughout that general region, and now notably destructive in 
sections of Missouri. At any rate this species of Clitocybe is very 
common at least from Missouri southwestvvard, and occurs abun- 
dantly in regions in which the root rot of apples is unknown. This 
fungus occurs, for instance, during a favorable season in unlimited 
quantity at Columbia, Mo., and may be found arising in large 
clusters from the roots of hickory and other deciduous trees ; but 
no evidence in that vicinity of its appearance in orchards has 
come to the attention of the writer, although constant search has 
been made for it, particularly where orchards have succeeded 




« 



Fig. 234. Clitocybe parasitica: a Cluster of Sporophores from 
Root of Hickory 



deciduous forests. The Clitocybe is unquestionably, however, an 
injurious fungus, and it is quite possible that the failure to attack 
apples in certain regions is due to more favorable conditions for 
the host. 

The fungus shown in Fig. 234 grows in very dense clusters. 
The pileus is usually from 6 to 8 cm. in diameter, convex or 
umbonate in form, usually beset with minute scales, varying in 
color from' mottled buff to pale yellowish brown. The gills are paler 
and become mottled, noticeably decurrent at first, which charac- 
ter is still slightly evident with age. The stipe is usually 10-16 cm. 
in length, and up to i cm. in diameter, solid, usually curved, and 



AUTOBASIDIOMYCETES 473 

somewhat darker in color than the i:)ileus. Rhizomorphs are pres- 
ent, and these, at maturity, are black in color. When growing; 
close beside the trunk or under the edge of fallen logs or brush, 
giant forms of the mushroom may appear, single specimens of 
which have been found weighing more than a pound, with gills 
anastomosing and variously modified. It has been suggested by 
some observers that Agaricus incllcits is responsible for this root 
rot of the apple, but the writer has never detected this fungus 
associated with the typical disease in Missouri. 

Control. It is hardly possible to adopt effective control measures, 
but it is desirable that every means possible be taken to get rid 
of stumps and roots in land set to an orchard, and preferably 
such land should be grown to some grain or other field crop for 
several years previous to its use for orchard purposes. Isolation 
of affected trees by trenching, and the prompt removal and de- 
struction of these, is also to be recommended. 

XIII. THE HONEY ACIARIC 

Annillaria nicllca Vahl. 

Hartig, R. Wichtige Krankheiten der Waldbaume. pp. 12-42. ph. /, 2. 
Hartig, R. Die Zersetzungserscheinungen d. Holzes d. Nadelholzbaume u. d. 
Eiche. Berlin, 1878. 

Of the Agaricaceae which may induce plant diseases there is no 
fungus better known or more destructive than Annillaria nirllca. 
It is abundant in Europe and America, and doubtless has a very 
general distribution. This fungus is unusual in that it is no less 
common as a saprophyte than as a parasite. It is said to occur 
upon all conifers which grow in Europe, and, among deciduous 
trees, especially upon Prniuis avium and Priimis domcstica. In 
moist regions it has been noted upon a variety of hosts, and in 
the small forests of central Missouri it has done greatest damage 
to young trees of the hop hornbeam {Ostrya virginiana) and of 
the white oak {Qjierais alba). It frequently attacks saplings, or at 
least its effects become evident upon such trees, of from i^ to 
3 in. in diameter. Infested trees grow very slowly, and often the 
leaves fall in early summer. When so far affected death promptly 
ensues. An examination of the crown of these trees would show 



474 



FUNGOUS DISEASES OF PLANTS 



a considerably advanced stage of decay in the region of the cam- 
bium, including both wood and bark. There is present an abundant 
white mycelium and very characteristic mycelial strands, as subse- 
quently described. 

The abundant, white mycelium is particularly rich in stored 
nutrients. It commonly extends several feet above the crown, 
mostly between the wood and bark. The characteristic mycelial 
cords, by which this fungus is best known, are shining, gray-black 




Fig. 235. Armillaria mellea on a Stump uf White Oak 
(Photograph by Geo. F. Atkinson) 

strands which may measure from i to 2I- mm. in diameter. They 
are typical rhizomorphs. These begin as complex hyphal masses 
which become readily sclerotial in character. These strands attain 
enormous lengths. They may course upward and downward in the 
affected tree, generally under the bark, or merely in close contact 
with the outer surface of the bark. They also grow through the 
soil to considerable distances, thus serving to spread the disease 
to neighboring trees. According to Hartig this strand is differ- 
entiated near the apex into several layers. The outer, more gelati- 
nous layer becomes somewhat horny ; some loose hyphae, however, 



AUTOBASIDIOMYCETES 475 

extend outward, perpendicular to this sheath. Within this zone 
there is next found a dense, resistant layer of small-celled pseudo- 
parenchymatous tissue, surrounding a medullary cylinder com- 
posed of lighter, more delicate, conducting cells. At the base of 
the tree the general mycelium produces a definite white rot. 

In this country sporophores are usually produced during favor- 
able weather in September, October, and early November. They 
may appear at the collar of the tree, or upon the roots, etc. More- 
over, a year or two after forest land has been cleared for pasturage, 
the sporophores may appear in enormous quantities on the slightly 
sunken roots. These fruit bodies are usually produced in clusters, 











.^ M 








^t 


I 


fti&^^i 


^ 

^ 


1^ 


fi 










v«^^ 


\^m 


<^v - 


1 



Fig. 236. Armillaria mellha on exfused Ruots in a Meadow 

arising either directly from a felted mycelium or from rhizomor- 
phal aggregations. The mature sporophore (Fig. 236) consists of 
a fleshy cap, ordinarily 5-15 cm. broad, borne upon a central stalk 
often 12-18 cm. long, with cartilaginous rind and spongy center. 
The stem is yellowish in color above, but usually brown below, with 
a more or less persistent annulus, or attached collar. The cap varies 
from convex to slightly umbonate. It is yellow to orange-brown in 
color, the center of the cap when younger being often covered with 
papilliform, brown, or sooty scales. The lamellae are white or slightly 
discolored, distinct one from another, and somewhat decurrent upon 
the stem. In taste this plant is distinctly acrid, sometimes very- 
harsh. It is, however, considered to be edible by those who have 
developed a taste for a variety of mushroom flavors. 



476 FUNGOUS DISEASES OF PLANTS 

With reference to the development of the sporophore, the early 
studies of Hartig would indicate that it begins as an ovoidal or 
spheroidal body, made up of closely united hyphae, the direction 
of whose growth is soon mostly longitudinal. For some time there 
is no differentiation of stem and cap, but after the hyphal mass has 
attained a length of several millimeters, differentiation into these 
parts becomes evident. In the first place, an annular furrow is 
formed by cessation of growth in certain filaments near the apex, 
and this annular furrow delimits pileus and stipe. Subsequently, 




Fig. 237. Armillaria mei.lea: Rhizomorphs and Young Spuruphores 
(Photograph by H. H. Whetzel) 

the outer layer of filaments from below and from above this fur- 
row become interlaced, and thus is formed an early stage of the 
veil, or membrane, inclosing the area in which the hymenium is 
eventually produced. As growth proceeds, the overlapping periph- 
eral elements become wholly indistinguishable, the pileus is then 
developed by successions of epinastic and hyponastic growth, the 
principal growth being in the direction of the pileus. The hy me- 
nial surface is thereafter differentiated by the growth downward of 
alternating radial hyphal bands, which form the trama, or middle 
tissue of the lamella, bearing eventually the hymenium or surface 
from which the basidia are produced. With the rapid growth in 



AlITOBASIDIOMYCETES 477 

the lower, or lamellar, portion of the pileus, the cap is quickly raised 
and the veil broken at the margins of the pileus, with the gradual 
expansion of the upper portion of the plant. This general form of 
development apparently maintains in most angiocarpic Agaricacese 




Fig. 23S. Armfllaria j/£iz.£.-/ .• Basidial Surface. (After Ilartig) 

which possess a veil only. Differences occur, however, with regard 
to the time of differentiation, position of the forming lamellae, the 
stem, veil, etc. 

XIV. EUROPEAN ROOT DISEASE OF ALFALFA AND 
OTHER PLANTS 

Rhizodonia Medicaginis De C. 

Frank, A. B. Die Pilzparisitaren Krankheiten der Pflanzen, /. c, pp. 5 14-5 rS. 

KiJHN, J. Die Kranklieiten der Kulturgewachse, /. c, p. 245. 

TuLASNE, L. R. and C. Rhizoctonia. Fungi Hypogaei, I.e., pp. 188-195, 

De Candolle described accurately the root disease of alfalfa 
{Mcdicago sativd) in 181 5, and gave to the violet fungus pro- 
ducing the disease the name above indicated. The fungus had 
previously passed under another name, which, however, probably 
referred to several diverse species. From the subsequent work of 
Klihn, Frank, Comes, and others, much additional information has 
been presented concerning this fungus. Many, however, have re- 
garded it as closely related to certain sterile fungi found upon 
the crocus, potato, cabbage, sugar beet, and many other cultivated 



478 



FUNGOUS DISEASES OF PLANTS 



and wild plants. The last-mentioned fungi are at least closely 
related, perhaps forms of a single species ; and in this treatise 
they are provisionally referred to the genus Corticium. They have 
been discussed under Corticium vaginn B. & C, var. Solani Burt. 

The writer examined various 
diseases due to Rhizoctonia 
while in Europe during 1899 
and 1900, and subsequently 
in the United States. As a 
result, certain observations 
may be stated. In the first 
place, the common alfalfa 
root fungus of Europe {Rhi- 
zoctonia Medicaginis) is the 
same as the European root 
fungus of asparagus {Aspara- 
gus offLcinalis). This species 
also occurs less frequently 
upon the sugar beet {Beta 
"oulgaris), and, doubtless, 
upon other cultivated and 
wild plants. The fungus ap- 
pears upon the root as a close 
weft of violet-colored hyphae 
(Fig. 239), composed of cells 
more or less uniform in diam- 
eter, filamentous, branched, 
but without a particularly 
characteristic type of branch- 
ing. Morphologically, it 
bears no resemblance to the 
sterile stage of Corticium 
vagum, above referred to, 
that is, the form causing the rot of the crocus, and a similar disease 
of the carrot, etc., in Europe, the rot of beets, stem rot of carna- 
tions, certain damping-off diseases, etc., in America. 

Rhizoctonia Medicaginis does not occur in America so far as 
can be ascertained. In Europe it is one of the most destructive 




Fig. 239. Rhizoctonia Medicaginis on 
Roots of Asparagus 



AUTOBASIDIOMYCETES 479 

of the clover diseases and frequently becomes epidemic in planta- 
tions of alfalfa, or lucern, a highly important forage plant of 
Central Europe. In asparagus growing the losses are also occa- 
sionally severe. 

An ascomycetous fungus occurring upon the stubble of alfalfa, 
described as Lcptosphceria circinans Fckl., has been by some re- 
garded as the perfect stage of RJiisoctonia Medicaginis, yet 
through cultures of ascospores the writer has been unable to pro- 
duce a mycelium resembling that of the Rhizoctonia, Moreover, 
the mycelium of the Rhizoctonia has been unusually difficult to 
propagate in artificial cultures, 

XV. ROOT ROT OF COTTON AND ALFALFA 
Ozonium onmivorum Shear 

Atkixsox, Geo. F. Method for Obtaining Pure Cultures of Pammel's Fun- 
gus of Texas Root Rot of Cotton. Bot. Gaz. 18 : 16-19. 1893. 

Pammel, L. H. Cotton Root Rot. Texas Agl. Exp. Sta. Rept. 2: 61-86. 
1889. (Also published as Built. 7: 1-30. 1889.) 

Shear, C. L., and Mn.p:s, G. F. The Control of Texas Root Rot of Cotton. 
Bur. Plant Ind., U. S. Dept. Agl. Built. 102 (Pt. 5): 39-42. 1907. 

In Texas and other neighboring states a serious root rot of cot- 
ton {Gossypinm spp.) and alfalfa {Mcdicago sativa) has been known 
for a number of years. It is not, however, confined to these hosts, 
and among cultivated plants the sweet potato {Ipomcra Batatas) is 
also affected. Pammel in 1 889 reported it on ten or more deciduous 
trees and also on a few herbaceous weeds. During the summer of 
1 90 1 I found this fungus on twelve different weeds in a single 
cotton field near Paris, Texas. Since these hosts represent a 
number of widely separated orders, it is apparent that the fungus 
is practically unrestricted. It does not, however, seem to occur 
upon monocotyledonous plants. 

Little is known about infection and the progressive stages of 
the disease. There is apparently very little evidence of the trouble 
until the plant suddenly wilts and dries up. It would seem that 
cotton plants are far more commonly killed after some of the bolls 
begin to mature. Certainly dead stalks become more evident from 
this time forward. Nevertheless, plants have been killed by the 
fungus before even any definite flower buds, or squares, have 



48o 



FUNGOUS DISEASES OF PLANTS 



1 



appeared. An examination of the plant after death shows that all 
of the smaller roots have been killed, and these readily break off 
as the plant is pulled from the soil. At this time the main root 
as well as the fibrous root system is infested with a weft, or with 
strands, of the dirty yellow or buff-colored fungus. 

The mycelium penetrates the bark and also the wood of the 
roots. It does not, however, extend into the wood far above the 

surface of the soil. This 

organism in the United 
States was first studied by 
Pammel and provisionally 
referred by him to the ster- 
ile form Ozonijini aurico- 
Diinn Lk, He seems to 
have had doubt of the cor- 
rectness of this reference 
from the beginning, and 
Shear now regards this 
American fungus as one 
clearly distinct from 
Link's species, and he has 
accordingly given it a new 
specific name, as above. 

This fungus may be 
grown on cooked potato 
and other nutrient media, 
but the organism is none 
too readily isolated. No 
spore stage has been found 
in culture, nor definitely 
associated with it in the 
open. A careful study of 
the organism in the field has given indications, however, that an 
oidium stage may be developed under certain conditions, and that 
the organism is probably a Basidiomycete. 

It seems that no successful inoculation experiments have been 
reported with this fungus. During two seasons I attempted to 
transfer the disease to potted cotton plants in the greenhouse. 




Fig. 240. OzoNiiM omxivorv.m ijn Rduts 
OF Cotton 



AUTOBASIDIOMYCETES 481 

Diseased roots of cotton and alfalfa, showing an abundance of the 
fungus, were placed beneath the soil in contact with the healthy 
roots of half-grown plants. In every case the fungus failed to 
spread, and after a few months seemed to be dead. These experi- 
ments, however, were merely preliminary, and the conditions under 
which the tests were made could not be considered satisfactory. 

Control measures. Control measures, according to Shear, should 
concern themselves primarily with proper aeration of the soil, espe- 
cially deep preparation and as close cultivation as may be compatible 
with other requirements. Fall plowing, under circumstances where 
this can be practiced without injury to the land, is advised. This 
is particularly applicable when short rotations are impossible. 
Rotation of crops is especially important. Grain crops and others 
known to be free from the fungus should alternate with cotton. 
An application of a fungicide to the soil at the time of planting 
seems to be neither effective nor practicable. 



I 



HOST INDEX OF FUNGOUS DISEASES SPECIALLY 
DESCRIBED OR CITED 

Acacia {Acacia spp.) Page 

Rust, Uroiiiyccs tepperianns Sacc 393 

Alfalfa (Medicago sativa L.) 

Anthracnose, Colletotrichum Trifolii Bain 328 

Leaf Spot, Psetcdopeziza Medicaginis (Lib.) Sacc 203 

Root Gall, Urophlyctis Alfalfce (v. Lagerh.) Magn 140 

Root Disease, European, Rhizoctoiiia Medicaginis De C 477 

Root Rot, Ozonittm oiiinii'OJ-um Shear 479 

Ambrosia {Ambrosia spp.) 

Leaf Blight, or Smut, Entyloma compos itanini P^arl 381 

Almond (Prunus Amygdalus Baill.) 

Crown Gall, Psciidoinoiias tiimefacieiis Erw. Smith & Townsend ... 114 

Leaf Blight, Cercospora ci>xitmscissa Sacc 314 

Rust, Pitccinia Priini-spinoscE Pers 417 

Ampelopsis {Ampelopsis spp.) 

Leaf Spot, Phyllosticta Antpelopsidis Ell. Sa Mart 347 

Anemone {Anemone spp.) 

Ti ^ ( Piicciitia fusca Relhan 422 

\Pi(ccinia Priini-spiiioste Pers. 417 

Sclerotial Disease, Sclerotinia tiiherosa (Hedw.) Fckl 201 

Apple (Pyrus Malus L.) 

Anthracnose, or Bitter Rot, Glomerella rufomacitlans (Berk.) Spauld. & 

von Schrenk 271 

Baldwin Fruit Spot, Cylindrosporium Poini Brooks 341 

Black Rot, Sphcs)vpsis Malorum Pk 350 

Blight, Fire Blight, Twig Blight, Bacillus amylovoriis (Burr.) I-)e Toni . 121 

Blotch, Phyllosticta solitaria E. & E 346 

'Bacillus amylovoftis (Burr.) De Toni 121 

Xectria cinnabarina (Tode) Fr 239 

Xectria ditissima Tul 242 

.Vnmniiclaria discreta Tul 282 

Sphceropsis Malorum Pk 350 

Crown Gall, Pseiidomonas tumefaciens Erw. Smith & Townsend ... 114 

Decay, or Brown Rot, Polyporus s7ilphureus (Bull.) Fr 457 

Fly Speck, Leptothyriitm Pomi (Mont. & Fr.) Sacc 367 

Fruit Mold, or Brown Rot, Sclerotinia fnictigena (Pers.) Schroet. ... 187 

Leaf Spot {P'^y^^o^^''^^^^ Pyrina Sacc 347 

\Sphcei-opsis Malontm Pk 350 

Pink Rot, Cephalothecium rosetitn Cda , 29^ 

483 



Canker 



484 HOST INDEX OF FUNGOUS DISEASES 

Page 
Apple [Pyrus Mains L.) {Continued) 

, M'M ( Podosp/nrra OxyacantAce (T)&C) De Bary .... 226 

y^Podosphcvra leucotricha (Ell. & Ev.) Salm 226 

Root Rot, Clitocybe parasitica Wilcox 471 

p ( Gymnosporangiiim tnacropits Lk 425 



Rust J 9""'^'^ 
\Gymnc 



losporangiiifn glob'osum Farl 426 

Scab, Veitturia Pomi (Fr.) Wint 264 

Sooty Blotch, Leptothyrinm Pomi (Mont. & Fr.) Sacc 367 

Spongy Dry Rot, VoliUella fnicti Stevens & Hall 316 

Apricot {Prunus Armeniaca L.) 

Black Knot, Plotvrightia niorbosa (Schw.) Sacc 24S 

Brown Rot, Sclerotinia fnutigena (Pars.) .Schroet 187 

Crown Gall, Pseicdonionas tiimefaciens Erw. Smith & Townsend ... 114 

Rust, Piiccinia Prutii-spinosa; Pers 417 

Scab, or Peach Scab, Cladosporiiim catpophilum Thiim 299 

Arbor Vitae {Thuja occidentalis L.) 

Root Rot, Polyponis Schweiiiitzii Fr 463 

Artichoke, Jerusalem {Helianthus tuberosus L.) 

Mildew, Plasiiiopara Halstedii Farl 161 

Rust, Piiccinia Helianthi Schw 420 

Ash {Fraxinus spp.) 

Decay, or Brown Rot, Polyponis snlphitrcus (Bull.) Fr 457 

Rot, Polvporus pyaxinophiliis Pk 464 

White Rot, Polyponis sqiiamosus (Huds.) Fr 453 

Asparagus (Asparagus spp.) 

Damping-off, or Rhizoctonia, Corticitim vagiim B. & C, var. Solan i Burt 444 

European Root Disease, K/iizoctonia Medicaginis De C 477 

Rust, Piiccinia Asparagi De C 403 

Aster {Aster spp.) 

Leaf Blight, or Smut, Entyloma compositarnin Farl 38 1 

Rust, Coleosporiitin Solidaginis (Schw.) Thiim 435 

Aster, China {Callistephus hortensis Cass.) 

Root Rot, or Rhizoctonia, Coriicium vagiitn B. & C, var. Solani Burt . 444 

Wilt, Fiisaj-iiim sp 320 

Balsam {Abies balsamea (L.) Mill.) 

Decay, F'otnes Pinicola Fr 467 

Barberry {Berberis spp.) 

Piiccinia graminis Pers 4°^ 

Barley {Hordeum spp.) 

Ergot, Claviceps purpurea (Fr.) Tul 244 

Tj ^ Piiccinia graminis Pers 4°^ 

yPuccinia nibigo-vera (De C.) Wint 416 

Smut, Ustilago nuda (Jens.) Kell. & Sw 377 



HOST INDEX OF FUNGOUS DISEASES 485 

Pace 
Barnyard Grass (Echinochloa crusgalli (L.) I'.eauv.) 

Smut, Tolyposporiiiiit hiillatitiii (Schroet.) Schroet 378 

Basswood [Tilia spp.) 

Anthracnose, Glaosporiiiin Tiliir Oudem 335 

White Rot, Polypoms xijnamosiis (Iluds.) Fr 453 

Bean (Phaseolus vulgaris L., P. lunatus L., etc.) 

Anthracnose, Colletotrickiini Lijidemiithiaiiiim (Sacc. & Magn.) Bri. & 

^av ■ • •. ^-- 

Blight, l^'sciidoiiionas Pliascoli Erw. Smith 119 

Damping-off, Pythiitm de Ba/yaiitim Hesse 141 

Downy MWdevi, P/tytop/it/io?-a P/iaseoli TYiaiitev 171 

Powdery Mildew, Erysiphe Polygoiii De C 227 

Rust, Uromyces appendiatlatics (Pers.) Lev 397 

Stem BHght, Root Rot, or Rhizoctonia, Corticiiim vugiirn B. & C, var. 

Solaiii Burt 444 

Beech {Fagus grandifolia Ehrb.) 

Decay, Fames fomentarius (L.) Fr 467 

Heart Rot, Fames igniarins (L.) Gillett 465 

Seedling Disease, Phytaphthora cactonmi (Leb. & Cohn) Schroet. . . 173 

Beet {Beta vulgaris L.) 

European Root Disease, Rhizoctonia Aledicaginis De C 477 

Gall, Uraphlyctis leptvides (Trabut) Magn 140 

Heart Rot, Phoma Beta Frank 343 

Leaf Blight, Cercospora Beticala Sacc 309 

Root Rot, or Rhizoctonia, Carticium vagiim B. & C, var. Solani Burt . 444 

Rust, Uromyces BetcE (Pers.) Kiihn 399 

Scab, Oospora scabies Thaxter 290 

White " Rust," C]'j/('///J />'//■/■/ (Biv.) Lev 152 

Bent Grass [Agrostis spp.) 

Rust, Puccinia gi-ami)tis Pers 408 

Bilberry {Vaccinium Myrtillus L.) 

Sclerotial Disease, Sclerotiiiia baccanim Schroet 195 

Birch (Betula sp.) 

Decay, Fames fomentarius (L.) Fr 467 

Heart Rot, Fames igniaritis (L.) Gillett 465 

Sapwood Decay, Polypoms Betiilinns (Bull.) Fr 464 

Sclerotial Disease, Sclerotinia Bettilcs Wor 201 

Blackberry {Rubus spp.) 

Anthracnose, Glaasporium I'cnetiiin Speg 334 

Cane Blio-ht J' '"""'"''^'''-'''''''""^ '^"^"'^'^''" ^^'^'^ ^54 



Leptosphceria Cofiiothyrium (Fckl.) Sacc 356 

Crown Gall, Pseudomonas ttime/aciens Erw. Smith & Townsend . . . 114 

GdiW, or Chytr\A\os&, Pycnochytriiim globasnin Schroet 139 

Leaf Spot, Septoria Rubi West 363 

Rust, Gymnoconia Peckiana (Howe) Tranz 427 



486 HOST INDEX OF FUNGOUS DISEASES 

Page 

Bluegrass {Poa spp.) 

^ Claviceps niicrocephala (Wallr.) Tul 247 

Ergot ■{ Claviceps pu7-purea (Fr.) Tul 244 

X^Claviceps setiilosa (Quel.) Sacc 247 

Rust, Piiccinia s^raminis Pers 408 

Blue-Stem Grass {Andropogon spp.) 

'>mut., Soivsporiiim Syiitke}-ismcE {V\f:..) Farl 378 

Bog Bilberry (Vaccinium uliginosum L.) 

Sclerotial Disease, Sclerotiiiia heteroica Wor. & Nawasch 195 

Borage {Anchusa spp.) 

Brown Rust, Puccijiia j-ubigo-vera (De C.) Wint 416 

Brome Grass {Bromus spp.) 

Rust, Piicci)iia gramhiis Pers 408 

Buckwheat [Fagopyrum esculentum Moench.) 

False Mildew, or Leaf IJlight, Raiiinlaria i-iifomacithnis Pk 297 

Buttercup {Ranunculus spp.) 

Leaf Spot, or Smut, Entyloma Kaniiiiciili (lion.) Schroet 381 

Butternut [Juglans cinerea L.) 

Anthracnose, Glaosporiiim Jitglandis (Lib.) Mont 335 

Decay, or Brown Rot, Polyponis sulp/iiireiis (Bull.) Fr 457 

Cabbage, Cauliflower, etc. (Brassica oleracea L.) 

Black Rot, Pseudotnonas campcstris (Pammel) Erw. .Smith 107 

Club Root, Plasmodiopho7-a Brassicce Wor 97 

Downy Mildew, Pero7iospo7-a parasitica (Pers.) De Bary 161 

Root Rot or Stem Rot, Rhizoctonia, Corticiiim vagiiui B. & C"., var. 

Solani Burt 444 

Soft Rot, Bacillus carotoz'oriis Jones 131 

White Rust, Cystoptis caiididits (Pers.) Lev . 149 

Calla (Zantedeschia athiopica (L.) Spreng.) 

Soft Rot, Bacillus aivideiE Townsend 133 

Canada Thistle {Cirsium arvense (L.) Scop.) 

Rust, Puccinia suaveolciis (Pers.) Rostr 421 

Carnation {Dianthus Caryophyllus L.) 

Anthracnose, / ('////t-//<? /J*/(?«//// Atkinson 317 

Bud Rot, Spomtrichum Poa Pk 293 

Leaf Spot, Septoria Dianthi Desm 363 

Root Rot, or Rhizoctonia, Corticium vagitin B. & C, var. Solaiii Burt . 444 

Rust, Uromyces Caiyophyllimis (Schrank) Wint 399 

Wilt, Fii sarin lu sp 321 

Carrot {Daucus Carota L.) 

Root Rot, or Rhizoctonia, Corticium vaguvi B. & C, var. Solani Burt . 444 
Soft Rot, Bacillus caroto7'orus Jones 131 

Catalpa (Catalpa Bignonioides Walt.) 

Leaf Blight, Macrosporium Catalpa Ell. & Mart 347 

Leaf Spot, Phyllosticta Catalpa Ell. & Mart 347 



HOST INDEX OF FUNGOUS DISEASES 487 

Cauliflower. .S',v Cabbage. ^'^'^^ 

Cedar, Red (Juniperus spp.) 

Peckiness, or Red Rot, Polyporus cartieus Nees 463 

{Gymiiosporajtgium globosiim Farl 426 

Gymnosporaiigiiim macropus Lk 425 

Gymnosporangium Sabinct Plowr 426 

White Rot, Polvponis Jiniipcrinits von Schrenk 463 

Celery (Apium graveolens L.) 

Damping-off, or Rhizoctonia, Coriicium vagiim B. & C, var. Solan i liurt 444 

Early Leaf Blight, Cercospora Apii Fr 312 

Late Blight, Septoria Petroselini Desm., var. Apii Br. & Cav 361 

Chard [Beta cyda L.) 

Leaf Spot, Ce?rospo>-a Beticola Sacc 3°9 

Chenopodiaceae 

Leaf Gall, 6^r^////i'<V/.s' /////('«)' (Wall.) Schroet 140 

Cherry {Prunus spp.) 

Black Knot, Phnvrightia morbosa (Schw.) Sacc 248 

Brown Rot, or Fruit Mold, Sclerotinia fntctigena (Pers.) Schroet. ... 187 

Crown Gall, Psetidomoiias tiimefaciens Erw. Smith & Townsend . . . 114 

Decay, or Brown Rot, Polyporus siilphtireus (Bull.) Fr 457 

Leaf Curl and Witches' Broom, Exoascics Cerasi Fuckel 185 

T f '^ (• j Cylind/vsporinm Pad i 'K.a.r si 339 

\Mycosph(P7-ella Cerasella Aderh 263 

Powdery Mildew, /"(Ji/^Jj/Z/f^pra Cxj'd'caw/'/^w'' (De C.) I)e Bary 226 

T, ^ r, ^ ^ Annillaria niellea Vahl 473 

Root Rot < ^,. , . . ,,,., 

\Clitocybe pa)-asitica Wucox 471 

Rust, Pticcinia Pntni-spinosie Pers 41? 

vScab, Cladosporium carpophilum Thiim 299 

Shot Hole, Cercospora circiimscissa Sacc 314 

Chestnut (Castanea spp.) 

Bark Disease, or Canker, Diaporthe parasitica Murrill 281 

Crown Gall, Pseudomonas iumefacietts Erw. Smith & Townsend . . . 114 

Leaf Spot, or Anthracnose, Marsonia ochroleiica B. & C 336 

Chrysanthemum (Chrysanthemum spp.) 

Crown GsH, Psetedomoftas tume/aciens TLrw. Smith & Townsend . . . 114 

Leaf Blight, Cylindrosporitun Chn'santhemi Ell. & Dearn 343 

Leaf Spot, Septoria Chrysanthemi Cav 3^4 

Rust, Pitccinia Chrysanthemi Roze 4^1 

Clover [Trifolium spp.) 

Anthracnose, CoUetotrichnm Trifolii Bain 328 

Damping-off, Pythiurn de Baryannm Hesse 141 

\.t.2l S^ot, Pseudopeziza Trifolii [Vers.) Yz\.\ .204 

Rust, Uromyces Trifolii (Hedw.) Lev 395 

Sooty Spot, Polythriticiitm Trifolii Kze 298 

Stem Rot, Sclerotinia Trifoliortim Eriks 201 



488 HOST INDEX OF FUNGOUS DISEASES 

Cocklebur (Xanthium spp.) ^^^^ 

Kust, PitLciiiia Xaiithii Schw 393 

Coffee (Coffea arabica L.) 

Rust, Ilemileia vastatrix Berk. & Br 393 

Cordyline (Cordyline spp.) 

Leaf Spot, Phyllosticta iiiaculiiola Hals 347 

Corn {Zea mays L.) 
Blight. See Wilt. 

Damping-off, Pythiiim de Baiyaiitn/i Hesse 141 

Downy Mildew, Sclerospora macrospora Sacc 161 

Rust, Piiccinia Sorghi Schw 414 

Smut [Ustilago Zece {?,^zVm.)\:n^ 376 

^^ Ustilago Reiliaiia Kiihn 377 

Wilt, Pseudomonas Stewarti Erw. Smith 1 1 1 

Cotton (Gossypium spp.) 

Angular I^eaf Spot, Pseudomonas inalvaceariim Erw. Smith 121 

Anthracnose, Colletot7-ichiim Gossypii Southworth 325 

Black "Rust," Macrosporiiitn tiigricantiiifn Atk 304 

Uamping-off, Sore Skin, or Rhizoctonia, Co7-ticiiim vagictn B. & C, var. 

Solaiii Burt 444 

False or Areolate Mildew, Ramularia areola Atk 296 

T r o i t:>i- u^ ( Cercospora Gossypiiia Cke 313 

Leaf Spot, or Blight ^ ,, ^ . , 

\^Sph(Erella Gossypina Atk 313 

Root Rot, Ozoniitm omnivo7iim Shear 479 

Wilt, or P'renching, Neocostnospora vasinfecta (Atk.) Erw. Smith . . . 233 

Couch grass [Agropyron repens (L.) Beauv.) 

Rust, Pucciiiia gramiiiis Pers 408 

Cowberry {Vaccinum Vitis-Id&a L.) 

Gall, Exohasidium Vaccinii {Y<:i\i\.) Wor 440 

Sclerotial Disease, Sclei-otiiiia Vaccinii Wor 195 

Crab grass {Panicum sanguinale L.) 

Leaf Spot, or Blast, /^/;7<;v^/(/;-M,{,'-;7'jt77 (Cke.) Sacc 297 

Cranberry {Vaccinium spp.) 

Gall, Exohasidium J'aciiiiii (Fckl.) Wor 440 

Gall, or Chytridiose, Synchytrium I'acciiiii Thomas 13S 

Scald, Giiignardia Vaccinii Shear . . . 259 

Sclerotial Disease, Scleroiinia Oxycocci Wor 19S 

Spot, Pestalozzia Gnepini Desm., var. Vaccinii Shear 338 

Cress {Lepidium sativum L.) 

Damping-off, Pvtitinm de Batyainim Hesse 141 

Crowberry {Empetrum nigrum L.) 

Sclerotial Disease, Sclcrotinia megalospora Wor 195 



HOST INDEX OF FUNGOUS DISEASES 489 

Cucumber (Cucumis sativus L.) ^^'^^ 

Anthracnose, ColUtotrichicm Lagenariiim (Pass.) Ell. & Hals 330 

Blight, or Wilt, Bacillus tracheipkiliis Erw. Smith 129 

Damping-off, Pyihium de Baiyanum Hesse 141 

Downy Mildew, Plasmopara ciihensis (B. & C.) Humphrey 1 5S 

Powdery Mildew, Etysiphe Cichoracearum De C 228 

Scab, CladosporittDi Ciccitmerinnni Ell. & Arth 300 

Stem Rot, Sclerotiiiia Lihertiaiia Fckl 198 

Wilt. See Blight. 

Currant (Ribes spp.) 

Anthracnose, Pseiidopeziza Ribis Kleb 204 

Cane Blight, Nectria cinuaharina (Tode) Fr 239 

Cane Wilt, Dothiorella 364 

Leaf Spot, Septoria Ribis Desm 362 

Powdery Mildew, Spkarotheca Mors-uva (Schw.) B. & C 221 

(Cronartiitm Ribicola Fisch. de Waldh 433 

Rust -i Auidiicm Grossiilariir Schum 393 

[^Piiccittia Ribis De C 393 

Dracaena (Dracena spp.) 

Leaf Spot, Phyllosticta ntaciilicola Hals 347 

Eggplant (Solamtm Melongena L.) 

Blight, Bacillus solanacearum Erw. Smith 134 

Leaf Spot, Phyllosticta horiorum Speg 346 

Seedling Stem Blight, Phoma Solaiii Hals 345 

Elm {Ulmus spp.) 

Blister Canker, A'uniDiularia discreta Tul 282 

White Rot, Polyponis sqtianiosiis (Huds.) Fr 453 

Evening Primrose (CEnothera biennis L.) 

Gall, or Chytridiose, Sviichytriiirn fulgetis Schroet 139 

Fig [Ficus Carica L.) 

Rust, Urcdo Fici Cast 393 

Fir (Abies spp.) 

Rust, ^-Ecidiiim clatiiiitiii Alb. & Schw 393 

Flax (Linum spp.) 

Wilt, FiisariiDii Liiii Bolley 319 

Fleabane (Erigeron spp.) 

Leaf Blight, or Smut, Ktitvloiiia cotupositariDii Farl 381 

Foxtail {Setaria spp.) 

yiWdew, Sclcrospora gra/f/ii/iccda (Sacc.) Schroet 161 

Ginseng (Panax quinquefolium L.) 

Blight, Alteniaria Panax Whetzel 305 

Wilt, Fiisarium sp 320 



490 HOST INDEX OF FUNGOUS DISEASES 

Golden-rod {Solidago spp.) ^^"^"^ 

Red Rust, Coleosporium Solidaginis (Schw.) Thiim 435 

Rust, Uromyces Solidaginis (Somm.) Niessl 402 

Gooseberry [Rihes Grossularia L.) 

Leaf Spot, Septoria Kibis Desm 363 

Powdery Mildew, Sphcerotheca Mois-icvie (Schw.) B. & C 221 

_ ( ALcidium Grossularia: Schum 393 

\PHccinia Rib is De C 393 

Grape ( Vitis spp.) 

Anthracnose, Glaosporiiim ampelophagiim Sacc 332 

Black Rot, Gitignardia Bidwellii (Ell.) Viala & Ravaz 254 

Crown Gall, Pseiidoino7ias tiiinefaciens Erw. Smith & Townsend . . . 114 

Downy Mildew, Plasmopara Viticola (B. & C.) Berl. & De Toni ... 152 

Leaf Blight, Cercospora Viticola (Ces.) Sacc 314 

Powdery Mildew, Unciniila necator (.Schw.) Burr 229 

Ripe Rot, or Anthracnose, Glomerella riifomaailans (Berk.) Spauld. & 

von Schrenk 271 

Ti ^ -r. . { Armillaria melU'ci Vahl 473 

Root Rot < ^ , . TT ■ 

yDeviatopIiora iiccatnx liartig 321 

Grape Fruit {Citrus Decumana Lour.) 

.S'lV Orange. 

Ground Cherry (Physalis pubescens L.) 

Smut, Eiityloina F/iysalidis (Kalchbr. & Cke.) Wint 380 

Groundsel (Senecio spp.) 

Downy Mildew, Bremia Ladiica Reg 164 

Hawkweed {Hieracium spp.) 

Rust, Piicciitia Ilieracii (Schum.) Mart 422 

Hawthorn (Cratagus spp.) 

Blight, Bacillus amylovorus (Burr.) De Toni 121 

Rust, Gvmnosporangiiifn clavariaforme (Jacq.) Rees 426 

Hepatica (Hepatica acutiloba De C.) 

Rust, Piiiiinia Print i-spinoscc Pars 417 

Hemlock (Tsuga canadensis (L.) Carr) 

Decay, or Brown Rot, Polyponis .siilpliiircus (Bull.) Fr 457 

Dry Rot, Traiiictcs Pini {V,xo1.) Fr 467 

Hickory (Carya alba (L.) Koch) 

Root Rot, CI itocybe parasitica Wilcox 471 

Hog Peanut (Amphicarpa monoica (L.) Ell.) 

(iall, or C'hytridiose, Syiichytriiim dccipicns Farl 139 

Hollyhock [Alth&a rosea Cav.) 

Rust, Piicciitia nialvaceartiiti Mont 4^9 



« 



HOST INDEX OF FUNGOUS DISEASES 491 

Hop Hornbeam (Ostrya virginiana (Mill.) Koch) 

Root Rot, ArDiillaria mellea Vahl 473 

Horse-chestnut (JEsculus Hippocastanum \..) 

Leaf Blotch, Pliyllosticta Pavi,c Desm 345 

Horse radish (Cochlearia Armoracia L.) 

Brown Spot, Alteriiaria Brassicie (Berk.) Sacc 308 

Root Rot, Thielaviabasicola {V,.&LV,x.)Zo^i 210 

White " Rust," Cystopiis candidiis (Pers.) Lev 149 

Huckleberry (Gaylussacia, Vaccinium, etc.) 

(lall, K\-ol'as!diii»i racciiiii (Fckl.) Wor 44° 

Hyacinth (Hyacinthus orientalis L.) 

Bacteriosis, BaciUus llyaci)ithi-septicits Heinz 134 

Yellow Disease, rscudoiitotias Hyacinth i (Wakker) Erw. Smith . . . 120 

Juniper {Juniperus communis L.) 

Rust, Gymnospormi gilt 1)1 clai'ariu-fonne (Jacq.) Rees 426 

Knotweed {Polygonum spp.) 

Rust, rucciiiia Polygon i Pers 393 

Larch (Larix decidua Mill) 

Canker, Dasyscypha WillkoDnnii Llartig 202 

Decay, or Brown Rot, Polyporiis siilphureus (Bull.) Fr 457 

Dry Rot, Trametes Pini (Brot.) Fr 467 

Root Rot, Polyporiis Schweinitzii Fr 4^3 

Lemon (Citrus Medica var. Limon L.) 

Brown Rot, Pythiacystis Citrophthcra R. E. Smith 144 

Sooty Mold. See Orange. 

Lettuce [Lactuca sativa L.) 

Damping-off, or Rhizoctonia, Coiiiciitm -'agnm B. & C, var. Solan i Burt 444 

Downy Mildew, Bremia LacUica: Reg '64 

-p. ( Sclerotinia Libertiana Fckl 19^ 

\Sclerotifiia Fuckeliana De Bary 196 

Leaf Spot, Septoria amsimilis E. & M .......-• 3"3 

Rot. See Drop and Damping-off. 

Lilac (Syringa vulgaris L.) 

Powdery Mildew, Micro.spJurra Alni (Wallr.) Wint 228 

Lily {Lilium spp.) 

Botrytis, or Ward's Disease, Sclerotinia Fuckeliana De Bary . . . . 196 

Locust, Common (Robinia Pseudo- Acacia L.) 

Decay, or Brown Rot, Poly poms sulphureus (Bull.) Fr 457 

Magnolia {Magnolia grandiflora) 

Leaf Spot, Phyllosticta MagnoUce Sacc 347 

Mallow (Malvacea) 

Rust, Pnccinia tnalvacearnm Mont 4^9 



492 HOST INDEX OF FUNGOUS DISEASES 

Maple (^ccr spp.) Page 

Anthracnose, Ghvosporiicm apoc7yptiim E. & E 33c 

Decay, Foiiies fomejiiarius (L.) Fr 467 

Ga\\, or Chytr\d\ost, Pycnockytrium globositni Schroet 139 

Heart Rot ^^'""^^ igniarius (L.) Gillett 465 

\Hydnitin septentrionale Fr 452 

Leaf Blotch, or Black Spot, Rhytisma Aceri)iin)i (Pers.) Fr 208 

Powdery Mildew, Unciniila Aceris (De C.) Wint 231 

White Rot, Polyportis sqiiamosiis (Huds.) Fr 453 

Meadow Foxtail {Alopecurus pratensis L.) 

Rust, Pitccinia gratninis Pers 408 

Mints (Labiate) 

Rust, Puccinia Mentha Pers 407 

Morning Glory (ConvolvulacecE) 

White " Rust," Cys/opus coiivolvitlacearit di Otth 152 

Mountain Ash {Pyrus Aucuparia (L.) Ehrb.) 

Rust, GynDiosporangiiim globositm Farl 426 

Sclerotial Disease, Sclerotinia Auaiparia Ledw 195 

Mulberry (Morus sp.) 

Blight, Bacillus Citboiiiaiiiis Macch 134 

Muskmelon [Cucumis Melo L.) 

Anthracnose, Blight, Downy Mildew, Leaf Spot, Wilt. See Cucumber. 

Mold, Cladosporiii III Ciiciiiiieriiiiiiii Ell. & Arth 300 

Mustard (Brassica spp.) 

Black Rot, Pseiidomoiias campestris (Pammel) Erw. Smith 107 

Club Root, Plasmodiophora Brassicce Wor 97 

White " Rust," Cystopjis candidus (Pers.) Lev 149 

Oak [Quercus spp.) 

Anthracnose, Gnomoiiia J'ene/n (Sacc. & Speg.) Kleb 278 

Decay, or Brown 'KoX., Polyportis siilphiireiis (Bull.) Fr 457 

Heart Rot. Pomes igniarius (L.) Gillett 465 

( /\osellinia Quercina Hartig 280 

Root Rot <( Clitocybe parasitica Wilcox 471 

\Armillaria mellea Vahl 473 

White Rot, Polyporus sijiiaiiiosus (Huds.) Fr 453 

Oats (Avena sativa L.) 

(Puccinia coronata Cda 420 

Rust -| Puccinia gratninis Pers 408 

yPuccinia rubigo-vera (De C.) Wint 416 

^^^'^ ]^'^t'^('go AveiicE [V^xs.) ]&ns 372 

\Ustilago levis (Kell. & Sw.) Magn 373 

Okra {Hibiscus esculentus L.) 

Wilt, or Frenching, A'eocostnospora vasinfecta (Atkinson) Erw. Smith . 233 



HOST INDEX OF FUNGOUS DISEASES 49 



J 



Oleander (Nerium Oleander L 



Page 



Tubercle Disease 



' Psettdomonas Olea; (Krc.) Ttqv iiS 

PseiiJomonas tiitnefaciens Smith & Townsend . . . 114 

Olive (Olea europaa L.) 

Tubercle Disease, /'.t£V/(/<'W(;«(Zj' O/^-fS (Arc.) Trev 118 

Onion (Allium Cepa L.) 

Downy Mildew, Peronospora Schleideniana De Bary 162 

M.o\A.,MacrosporiumSarcintclaV>G.xV.,\2iX.parasiticiim'X^\\\.\m. 304 

Rust, Puccinia Allii De C . 393 

Smut, Urocystis Cepitl(V Frost 381 

Orange {Citrus Aurantium L., and C. nobilis Lour.) 

Brown Rot, Pythiacystis Citrophthora R. E. Smith 144 

Sooty Mold, Meliola CanielluF (Catt.) Sacc 213 

Wither Tip, Colletotrichinn Glaosporioides Penz 327 

Orchard Grass (Dactylis glomerata D.) 

T, ^ { Piiicifiia loroiiatd Cda 420 

Rust <!„..„ o 

y^Piiccnna graniniis rers 4°° 

Oxalis (Oxalis spp.) 

Rust, Puccinia Sorghi Schw 414 

Parsnip {Pastinaca sativa L.) 

Pearly Blight, Ccrcospom Apii Fr 312 

Pea {Pisum spp.) 

Powdery Mildew, Etysiphe Polygoni De C 227 

Root Rot, Thielavia basicola (B. & Br.) Zopf 210 

Rust, Uromyces Pisi (Vers.) De Bary 398 

Stem Rot, or Root Rot, Corticiiim vagiim B. & C, var. Solaiti Burt . . 444 

Peach {Prunus Persica Benth. & Hook.) 

Anthracnose, Gla:osporium UHicoIor Berk 335 

Blight, Coryneum Beijerinckii Oudem 336 

Brown Rot, Scleivtinia fructigena (Pers.) Schroet 187 

Crown Gall, /'.r«/(/<'/«^«rtJ- /^/w^i?"'^'" Erw. Smith & Townsend ... 114 

Frosty Mildew, or False Mildew, Cercosporella Persicce Sacc 297 

'L&dii Curl, Kvoasciis deformans (^erV.) ¥\ickt.\ 176 

-r, 1 AT-ij ( Spkcerotkeca patmosa (y<[a\\r.) 'Lev 224 

Powdery Mildew .^ ^ , , %^ ^7 /-nw >■ ^ t-v xj -,,r 

■' \PodosphcEra Oxyacatithce (De C.) De bary .... 22b 

Root Rot, Clitocybe parasitica Wilcox 47 1 

Rust, Puccinia Pnini-spinosa Pers 4^7 

Scab, Cladosporinm carpophilum Thlim 299 

Pear yPyrus communis L.) 

Blight, or Fire Blight 1 ^,,,,7/,,, ^,;,j,/^,,^„/. (Burr.) De Toni . ... 121 

Body Blight, or CankerJ 

Crown Gall, Pseudomo7tas tumefaciens Erw. Smith & Townsend. ... 114 

Decay, or Brown Rot, Polyporus sulphnrens (Bull.) Fr 457 

Leaf Blight, Entomosporiiim maculaUim Lev 365 



494 



HOST INDEX OF FUNGOUS DISEASES 



Ve&r {Pyrus communis I..) {Contimied) "^ 

Leaf Spot, Septo7-ia Pyricola Desm 358 

^ Gymiiospora?iginm clava7'ice/orme (]dLC(\.) Rees 426 

Rust < Gynutosporangium globosum Farl 426 

X^Gvmiiosporangiiim Sabina Plowr 426 

Scab, I'l-ii/itria Pyriiia Aderh 264 

Pepper (Capsicum annuum L.) 

Anthracnose, Colletotrichum nigrum Ell. «& Halsted . 330 

Persimmon {Diospyros virginiana I>.) 

Leaf Blight, Cciro.spora D i o.spy ri Th\im 315 

Pigweed {Amarantacea spp.) 

White " Rust," Cysiop/is B//1/ {W\v.) Lev 152 

Pine {Pinus spp.) 

Blight, Pestalozzia HaHigii Tub 339 

T^ Ti ^ {Fames Phticola Fr 467 

Dry Rot < ^ „. . ,^ ^ ^ / 

^ \T7-ametes Pint (Brot.) Fr 467 

Root Rot, Polyponis Schweitiitzii Fr 463 

•r, . { Coleosporium Solidaginis (Schw.) Thiim 435 

y^Cronartium Ribicola Fisch. de Waldh 433 

Plum {Prunus spp.) 

Black Knot, Plo-iorightia mcrhosa (Schw.) Sacc 248 

^X\^\\\., Bacillus amylovorus (Burr.) De Toni 121 

Brown Rot, or Fruit Mold, Sclcivtinia fructigeiia (Pers.) Schroet. . . . 187 

Crown Gall, Pseudomotias titmefacieiis Erw. Smith & Townsend . . . 114 

Leaf Spot, Cyli>id)vsporium Padi Karst 339 

Plum Pockets, Exoasais Pnuii Fuckel 183 

Powdery Mildew, Podosphara Oxyacanthct (De C.) De Bary 226 

Root Rot, Armillaria mellea Vahl 473 

Rust, Piiccinia Pntni-spinos(E Pers 417 

Scab, Cladosporiiim carpophilum Thiim 299 

Poplar {Populus spp.) 

Crown Gall, Pscudomonas tiimefacieiis Erw. Smith & Townsend . . . 114 

Decay, or Brown Rot, Polyponis sulphureits (Bull.) Fr 457 

Heart Rot, Fomes igniariiis (L.) Gillett 465 

Leaf Spot, or Anthracnose, Marsonia Popitli (Lib.) Sacc 336 

Powdery Mildew, Unciniila Salicis (De C.) Wint 230 

Rust, Melampsom trcmuLr Tul 437 

Poverty Grass [Aristida spp.) 

Smut, Sorosporiiim Syntherisma" (Pk.) Farl 378 

Potato {Solanum tuberosum L.) 

lilight, Baiillus .uda)iaccarum Erw. Smith 134 

Downy Mildew, or Dry Rot of Tubers, Phytophthoni iiifestaiis (Mont.) 

De Bary 165 

Dry Rot, or Stem Blight, Fitsarium oxysporum Schl 317 

Early Blight, Macrosporiiim Solani E. & M 301 

Rhizoctonia, or Scurf, Corticium vagum B. & C, var. Solani Burt . . . 444 

Scab, Oospora scabies Thaxter 290 



HOST INDEX OF FUNGOUS DISEASES 495 

Privet (Ligustrum vulgare L.) V\oe 

Anthracnose, Glaosporiiim ciiigulatuin Atkinson 335 

Pumpkin. See Squash. 

Quince (Cydonia vulgaris Pers.) 

Bitter Rot, Glomerella rufomacidans (Berk.) Spauld. & von Schrenk . . 271 

Black Rot, Sphccropsis Malorum Pk. . .• 350 

Blight, or Fire Blight, Bacillus amylovonis (Burr.) De Toni 121 

Leaf Blight, or Fruit Spot, Eiitomosporiiim maculatiim Lev 365 

Rust, Gymnosporaiigitim globosiini Farl 426 

Radish (Raphanus sativus L.) 

Club Root, Plasinodiophora Brassicce Wor 97 

Damping-off, or Rhizoctonia, Corticiu/n vagiim B. & C, var. Solaiii Burt 444 

Damping-off, Pythiiim de Baryaniim Hesse 141 

Downy Mildews, Peronospora parasitica Pers 161 

White " Rust," Cystopiis candidiis (Pers.) Lev 149 

Raspberry {Rubus spp.) 

Disease;;. .S'(V Blackberry. 

Rhododendron (Rhododendron spp.) 

Rust, Clnysomyxa Rhododendri (De C.) De Bary 432 

Sclerotial Disease, Sclerotinia Rhododendri Fischer 196 

Rice (Oryza sativa L.) 

Blast, Piriciilaria grisea (Cke.) Sacc 297 

Smut, Tilletia horrida Tak 3S0 

Rice, Wild (Leersia spp.) 

Smut, Tillclia corona Scrib 380 

Rose {Rosa spp.) 

Crown Gall, Pseiidoinonas tumefaciens Erw. Smith & Townsend ... 114 

Downy Mildew, Peronospora sparsa Berk 164 

'Leai }i\otc\\, Actinonema Rosce (lAh.) Fr 357 

Powdery Mildew, Spharotheca panitosa (Wallr.) Lev 224 

Rust, Phragmidiuin siihcorticiuni (.Schrank) Wint 430 

Rye (Secale cereale L.) 

Ergot, Claviceps purpurea (Fr.) Tul 244 

Powdery Mildew, Eiysiphe graminis De C 217 

Tj , \ Piiccinia graminis Pers 40S 

\^Pucciiiia nihigo-vera (De C.) Wint 416 

Smut, rrocystis occulta {\NdMr.) Reb 383 

Salsify (Tragopogon porrifolius L.) 

Rust, Pucci)iia Tragopogi (Pers.) Cda 421 

White "Rust," Cystopns Tragopogonis Pers 15- 

Shepherd's Purse (Capsella Bursa-pastoris) 

Club Root, Plasniodiophora Brass icic Wor 97 

Downy Mildew, Peronospora parasitica (Pers.) De Bary 161 

White " Rust," Cystopus candidus Lev 149 



496 HOST INDEX OF FUNGOUS DISEASES 

Snapdragon (Antirrhinum majus L.) Vf^Gu 

Anthracnose, Colletotrichiini Aiitirrhini Stewart 329 

Sorghum {Sorghum spp.) 

Rust, Pitcciiiia Sorghi Schw 414 

Smut, Ustilago Reiliana Kiihn 377 

Sorrel (Rumex spp.) 

Rust, Uromyces Ritmicis (Schum.) Wint 402 

Spinach {Spinacia oleracea Mill.) 

Downy Mildew, Peiviiospora effusa (Grev.) Rabh 164 

Spruce (Picea spp.) 

Decay, or Brown Rot, Polyporiis sitlphureiis (Bull.) Fr 457 

Drv Rot J^"'"^^ Pinicola Fr 467 

^ \Trametes Pini {^ro\..)Yx 467 

Root Rot [Pch'P^''"^ borealis (Wahl.) Fr 463 

\Polyponts Schweitiitzii Fr 463 

Rust, Chrvsomyxa Rhododendri (De C.) De Bary 432 

Spurge [Euphorbia spp.) 

., (Uromyces Pisi (Pers.) De Bary 398 

\^Uroinyces sciitcllatiis (Schr.) Wint 402 

Squash {Cucurbita spp.) 

Anthracnose, Blight or Bacterial Wilt, Downy Mildew, Fruit Mold, Pow- 
dery Mildew. See Cucumber. 

Root Rot, or Rhizoctonia, Corticiiim 7'agiim B. & C, var. Solaiti Burt . 444 

Star Cucumber (Sicyos angulatus L.) 

Downy Mildew, /Y(7JWi?/(7ra (■///'tv/.f/j (B. & C.) Humphrey 158 

Strawberry [Fragaria spp.) 

GdW, or Chyindiose., Pycfioc/iytrium glohosiim (Schroet.) Schroet. ... 139 

Leaf Spot, Mycosphirrella Fragaria (Tul.) Lindau 261 

Powdery Mildew, Spharotheca Hiimuli De C 226 

Sugar Cane {Saccharum qfficinarum L.) 

Bundle Blight, Psei/do//io//iJs vasculariDu (Cobb) Erw. Smith 120 

Leaf-splitting Blight, Mycospharella stratifornians Cobb 263 

Red Rot, Colletotrichiini falcaUcm Sacc 330 

T, ^ ... ( Marasmiiis plicatits Wakker 469 

Root Disease ^ ,, . „ , . ,,, , , ^ 

lA/arasm//is Sacchan Wakker 409 

Sunflower {Helianthus annuus L.) 

Damping-off, Pythium de Baiyaiiiim Hesse 141 

Downy Mildew, Plastuopara Halstedii Farl 161 

Rust, Pitccinia Helianthi Schw 4^0 

Sweet Potato (Ipomcea Batatas Lam.) 

Black Rot, .S//^«-;w/<'w,//?wA;7<7///w (Ell. & Hals.) Sacc 348 

Dry Rot, PJioma Baiatci Ell. & Hals 344 

Root Rot, or Rhizoctonia, Corticiiim vagiim B. & C, var. Solaiii Burt . 444 



I 



HOST INDEX OF FUNGOUS DISEASES 497 

Sweet Potato (Ipomosa Batatas Lam.) {Continued) ^^'^•^ 

Root Rot, Ozonium ot>Jtih'orum Shear 479 

Soft Rot, Rhizopus nigricans Ehr 349 

Stem Rot, Nectria Ipoma-ir Hals 243 

White " Rust," Cystopns con7<olviilaceartun Otth 152 



Sycamore (Platanus occidentalis T>.) 

Anthracnose, Gnoiiionia I'eneta (Sacc. & Speg 

Teosinte (Euchlcena luxurious l)ur. & Asch.) 

Smut, i'sti/iigo ZiiC (IJeckm.) Ung 



Kleb. 



Timothy (Phleum pratense L.) 

Ergot, Claviceps purpurea (Fr.) Tul 

Rust, Puccinia rklei-pratensis Eriks. & Henn. 



Tobacco {Nicotiana Tabacum L.) 

Damping-off, or Rhizoctonia, Corticiutn vagum B. & C 

Leaf Spot, Ceirospora A'icotiana E. & E. ... 

Powdery Mildew, Eiysiphe Cichoraceanim De C. 

Root Rot, Thielavia basicola (B. & Br.) Zopf . 

White Spot, Macrosporium Tabacinum Ell. & Ev 

Wilt, or Granville Wilt, Bacillus solanacearum Erw. Smith 



Solan i Burt 



278 



376 



244 
415 



444 
315 
228 
210 
304 
134 



Tomato (Lycopersicum esculentum Mill.) 

Anthracnose, Colletotrichum Phomoides (Sacc.) Chester 330 

Blight, Bacillus solanaceanc?n Erw. Smith 134 

Downy Mildew, Pkytophthora infestans (Mont.) De Bary 165 

Fruit Rot, JMacrosporium Solan i E. & M 3°' 

Leaf Mold, Cladosporium fulvum Cke 300 

Leaf Spot, Septoria Lycopersici Speg 362 

Rot (cause variously determined). 

Stem Rot, Corticiuin 7'agum B. & C, var. Solani Burt 444 

Sleepy Disease, or Wilt, Fusariuni Lycopersici Sacc 318 



Trumpet Creeper (Tecoma radicans (L.) Juss. 
Leaf Blight, Ccrcospora sonlida Sacc. . 



315 



Turnip (Brassica campestris L., and B. Rapa) 

Black Rot, Pseudomonas campestris (Pammel) Erw. Smith 107 

Club Root, Plasmodiophora Brassiae Wor 97 

Downy Mildew, /"£";-() ;/<7j/i()ra /(7rajV//V« (Pers.) De Bary 161 

Powdery Mildew, Eiysiphe Polygoni De C 227 

White " Rust," Cystopns candidus (F&rs.) Lev I49 



Verbena (Verbena spp.) 

Powdery Mildew, Eiysiphe Cichoracearum De C. 

Vetch (Vicia spp.) 

Powdery Mildew, Efysipike Polygoni De C. . . 
Rust, Uromyces Pisi (Pers.) De Bary .... 



228 



227 
398 



498 HOST INDEX OF FUNGOUS DISEASES 

Violet (r/o/a spp.) Page 

Gall, or Q.hytridlose., Fycfioc/iytn'iim globosinii (Schroet.) Schroet. . . . 139 

Leaf Blight, Cercospora Violie Sacc 315 

T r f . { Altcniaria Violce Gall. & Dorsett ^08 

Leaf Spot i „,,,.,., , -^ 

\^J nyllosttcta Violtz Desm 347 

Root Rot, Thielavia basicola (B. & Br.) Zopf 210 

Rust, Piicciiiia ViolcB (Schum.) De C 407 

Walnut (Juglans spp.) 

lilight, Psetidomojias Jiiglandis Pierce 120 

Crown Gall, Pseitdonionas tumefacietts Erw. Smith & Townsend ... 114 

Decay, Polypoi'iis siilphu7-eiis (Bull.) Fr 457 

Water Cress {Radicula Nasturtium-aquaticum (L.) Britten & Rendle) 

White " Rust," Cystopiis caiuiidiis (Pers.) Lev 149 

Watermelon {Citrullus vulgaris Schrad.) 

Anthracnose, Downy Mildew, Leaf Mold, Leaf Spot. Sec Cucumber. 

Damping-off, or Rhizoctonia, Corticium vagiim B. & C, var. So/a/// Burt 444 

Wilt, jVeocos/f/ospora vas/i/fecta (Atkinson) Erw. Smith 233 

Wheat {Triticum spp.) 

Ergot, C/av/ceps purpurea (Fr.) Tul 244 

( Pucc/n/a corotiata Cda 420 

Rust -i P/icc/n/a gram/n/s Pers 408 

y^Pucc/ii/a ncb/go-vera (De C.) Wint 416 

g^^j. ///■//^/■/a/a-^^wj (B.&C.) Trel 379 

Smut, loose, Ust//ago Tr/t/c/ (Pers.) Jens 375 

Wild Rosemary {Ledum palustre L.) 

Sclerotial Disease, Sc/crot/)//a hetero/ca Wor. «& Nawasch 195 

Wild Rye {Elymus spp.) 

Rust, P/tcc/i//a grami>//s Pers 408 

Willow [Salix spp.) 

Black Spot, Rhytisma Sa//c////i/// (Pers.) Fr 209 

Crown Gall, Pseudomonas tiiD/efac/ei/s Erw. Smith & Townsend ...114 

Decay, or Brown Rot, Po/ypor/(s sii/phure/is (Bull.) Fr 457 

Powdery Mildew, Uiic/mi/a Salicis (De C.) Wint 230 

White Rot, Polypoitis squamosus (Huds.) Fr 453 



GENERAL INDEX' 



Abies balsamea 467 

Acacia 393 

Acer 139, 185, 208, 231, 335, 454; sac- 

charum 453, 466, 467 
Actinonema Rosse 357 
Aderhold, R. 187, 263, 264 
^cidium, Berberidis 80; Oxalidis 415; 

punctatum 418 
^sculus 185, 345 
Agar agar 26 
Agaricacese 442 
Agaricus campestris 39, 56, 72 
Agropyron 410 ; repens 410 
Agrostis, canina 410; scabra 410; 

stolonifera 410 
Albuginaceas 148 
Alcohol, fixing agent 42 
Aleyrodes 214 
Algae 136 

Allium 393; Cepa 162, 304, 381 
Alnus 185 

Alopecurus pratensis 410 
Alternaria 2S8 ; Brassicae 308 ; Panax 

305 ; Violae 308 
Althaea rosea 419 
Amarantaceas 152 
Ambrosia 381 
Amelanchier 423 

Ammoniacal copper carbonate 89 
Ampelopsis, quinquefolia 314 ; Veitchii 

347 
Amphicarpa monoica 139 
Anaerobic bacteria, sterilization 18 
Anatomical effects 5 
Anchusa, arvensis 416; officinalis 416 
Ancylistales 135 
Andromeda ligustrina 441 
Andropogon 378 
Anemone 422; coronaria 418; nemo- 

rosa 201 
Angular leaf spot, cotton 121 
Anthracnose, beans 322 ; clover and 

alfalfa 328; cotton 325; currants 204; 

grape 332 ; raspberry and blackberry 

334 ; snapdragon 329 



Antirrhinum majus 329, 345 

Apium graveolens 312, 361, 447 

Aralia quinquefolia 211 

Aristida 378 

Armillaria mellea 322, 473 

Arthur, J. C. 121, 299, 339, 376, 384, 

388, 407, 414, 421, 435 
Ascomycetes 95, 174, 285, 331 
Asparagus, capsicus 405 ; maritimus 

405 ; officinalis 403, 444, 478 
Aspergillus 56; flavus 71 ; niger 71 
Aster 381, 435 
Atkinson, G. F. 79, 141, 175, 233, 312, 

313-321, 325' 335' 399. 444. 452, 457. 

463, 464, 479 
Atriplex 140 
Atwood, G. G. 434 
Autobasidiomycetes 439 
Autoclave 19 
Autoecism 387 

Avena, fatua 37 2; sativa 37 2, 4 1 2, 4 1 6,420 
Azotobacter chroococcum 74 

Bacillus 103, 106; amylovorus 107, 121 ; 
anthracis 71 ; aroideae 107, 133; caro- 
tovorus 107, 131 ; Cubonianus 107, 
134; Hyacinthi-septicus 107, 134; 
prodigiosus 33 ; solanacearum 107, 
134; tracheiphilus 107, 129 
Bacteria 82, 103; elimination of 36; 

staining 52 
Bacteriaceas 105, 106 
Bacterium teutlium 106 
Bain, S. M. 85, 328 
Bandi, W. 430 
Bark disease, chestnut 281 
Basidiomycetes 56, 95, 285, 439 
Beach, S. A. 119, 248, 264, 322, 361 
Begonia 211 ; rubra 211 
Benecke, W. 62 
Berberis vulgaris 410 
Bergamot oil 52 
Berkeley, M. J. i, 180, 445 
Beta, cycla 309 ; vulgaris 140, 291,309, 
446, 449, 478 

1 For common names of host plants and a list of the diseases of any host, see Host 
Index, page 4S3. 

499 



500 



GENERAL INDEX 



Betula 20I, 464, 467 ; lutea 466 
Bidens 161 
Bioletti, F. T. 229 
Black knot, plums 248 
Black rot, cabbage 107; grapes 254; 
pomaceous fruits 350; sweet potato 

348 
Black rust, grain 40S 
Black spot, maple 208 
Blackman, V. H. 384 
Blair, J. C. 271 
Blight, bean 119; canker 128; ginseng 

305 
Bolley, H. L. 319, 408 
Bonnet 11 
Boraginaceae 139 
Bordeaux mixture 7, 88, 92 
Botrytis 56, 69, 186, 287 ; cinerea 66, 

67,75, '97 5 Douglasii 196; vulgaris 

7I' 197 
Bouillon 24 
Brassica, campestris 99, 109, 149, 162, 

291; nigra 149; oleracea 99, 107, 

308, 449 ; Rapa 99, 149 
Brefeld, O. 3, 12, 94, 247,370,375,439, 

461 
Bremia 148 ; Lactucas 164 
Briggs, L. J. 210 
Britton, W. E. 22 
Bromus secalinus 410 
Brooks, Charles 341 
Brooks, F. T. 196 
Brown rot, conifers 467; lemon 145; 

stone fruits 6, 187 
Brown rust, wheat and rye 416 
Bud rot, carnations 293 
Buller, A. H. R. 453 
Bulliard, P. i 

Bundle blight, sugar cane 120 
Bunt, wheat 379 

Hurrill, T. J. 3, iii, 121, 215, 271 
Burt, E. A. 85 

Callistephus hortensis 320, 435 

Canker, blister 282; body 123; Euro- 
pean apple 242 ; larch 202 ; woody 
plants 239 

Capsella 162 ; Bursa-pastoris 99, 149 

Capsicum annuum 330 

Carbon, nutrition 73 

Carleton, M. A. 408 

Carpinus 185 

Carya 472 

Castanea, crenata 281; dentata 114, 
281, 336 

Catalpa 347 

Cedar apples 425 

Cenchrus 378 



Cephalothecium 287 ; roseum 295 

Ceratiomyxa loi 

Cercis canadensis 283 

Cercospora 288, 303, 314; Apii 312, 
361; Beticola 309; Cerasella 263; 
circumscissa 314 ; Diospyri3i5; Gos- 
sypina3i3; Nicotianae 31 5 ; sordida 
315; Violas 315; Viticola 314 

Cercosporella 288, 290, 297 ; Persicae 297 

Chamberlain, C. J. 41 

Chenopodiaceae 164 

Chenopodium 140 

Chester, F. D. 103, 201, 299, 301, 330 

Christman, A. H. 384, 395 

Chrom-acetic solution 43 

Chromic acid 43 ; cleaning mixture 13 

Chrom-osmo-acetic solution 44 

Chrysanthemum 343, 364, 421 ; frutes- 
cens 117; indicum 421 ; sinense 421 

Chrysomyxa 389, 390 ; Rhododendri 

432 
Chytridiales 63, 136, 139 
Cirsium arvense 422 
Citrullus vulgaris 129, 159, 233, 300, 

330, 449 
Citrus 144, 213, 327 
Cladosporium 287; carpophilum 299; 

Cucumerinum 300 ; fulvum 300 
Clark, J. F. 55, 85 
Classification, general 93 
Clasterosporium carpophilum 337 
Claviceps 232 ; purpurea 244 ; micro- 

cephala 247 ; setulosa 247 
Climatological factors 66 
Clinton, G. P. 158, 165, 171, 199, 210, 

264, 271, 356, 367, 370, 427, 435, 444 
Clitocybe 443 ; parasitica 471 
Close, C. P. 221 
Clove oil 51 

Club root, cabbage, etc. 5, 97 
Cobb, N. A. 120, 263, 357, 469 
Coccus 103 

Cochlearia Armoracia 149, 211, 30S 
Coenocentrum 151 
Coffea arabica 393 
Cohn, F. 10, 17 
Cold water box 29 
Coleosporiaceae 3S9 
Coleosporium 389,390,435; Solidaginis 

435 
Colletotrichum 289, 330, 332 ; Antirrhini 

329; falcatum33o; Gloeosporioides 

327; Gossypii325; Lagenarium 330 ; 

Lindemuthianum 322; nigrum 330; 

Phomoides 330; Trifolii 328 
Collodion 32 
Colony counting 36 
Combs 203 



GENERAL INDEX 



501 



Comes. O. 3, 93, 477 

Compositae 152, 161, 164, 435 

Conifers 454, 463 

Coniothyrium 290; Fuckelii 354 

Control, measures 7 ; methods 85 

Convolvulaceae 152 

Cooke, M. C. 94 

Coplin's staining jars 48 

Corda, A. C. i, 94 

Cordyceps 232, 286 

Cordyline 347 

Cornu, M. 3, 152 

Corrosive sublimate 43, 91 

Corticium 442 ; vagum var. Solani 79, 

212,444,478 
Coryneum 289 ; Keijerinckii 336 
Cover glasses, cleaning 14, 15 
Craig, John 295 
Crataegus 123, 423; monogyna 426; 

Oxyacanthae 426 ; tomentosa 426 
Crocus 478 
Cronartiaceae 389 

Cronartium 389, 390; Ribicola 433 
Crop rotation 87 
Crops, annual losses 7 
Crown gall, almond, apple, etc. 114 
Cruciferae 98, 141, 161 
Cucumis, Melo 300; sativus 129, 141, 

159' 330 
Cucurbita Pepo 449 
Cucurbitaceae 129, 159, 228 
Cugini, G. 161 

Culture media, preparation 23 
Culture methods 9 ; development and 

application of 10 
Culture room 60 
Cultures, sealing 39 ; by sporophore 

fragments 39 ; storage 38 
Cupressus 423 
Cyclamen 21 1 

Cydonia vulgaris 123, 365, 423, 426 
Cylindrosporium 289, 314; Chrysan- 

themi 343 ; Padi 314, 339 ; Pomi 341 
Cystopus, candidus 65, 81, 149, 157, 162; 

convolvulacearum i 52 ; Bliti 81, 152; 

Tragopogonis 152 
Cytospora 282 

Dactylis glomerata 410, 420 
Damping-off 141, 446 
Dangeard, P. A. 370, 393 
Darwin, Charles 168 
Dasyscypha 185; Willkommii 202 
Datura Stramonium 302 
Daucus Carota 131, 291, 449, 478 
Davis, B. M. 149 

De Bary 2, 12, 56, 69, 72, 94, 147, 165, 
186, 197, 215, 244, 370, 397, 398, 408 



De CandoUe 444, 477 

Decay, or brown rot 457 

Deciduous trees 458, 466 

Dematieae 2S7 

Dematophora necatrix 321 

Detmers, Freda 334 

Dianthus Caryophyllus 293, 317, 321, 
3<^3' 399' 478 

Diaporthe 254, 290; parasitica 281 

Diatrypaceae 175 

Dietel, P. 370 

Diospyros virginiana 315 

Discomycetes 174, 185 

Disease, control 3 ; European root 477 

Division of botany 4 

Dolichos ornatus 397 

Dothidiaceae 175, 248 

Dothiorella 364 

Downy mildew 148; crucifers 161 ; cu- 
cumbers I 58 ; grape 152; lettuce 1 64 ; 
lima beans 170; onion 162, 304 

Dracaena 347 

Drop, lettuce 198 

Dry rot, potatoes 317; sweet potatoes 
344 

Dudley, W. R. 204, 261, 419 

Duggar, B. M. 55, 71, 264, 312, 358, 361, 

365^ 444 
Durand, E. J. 239 

Early blight, celery 312 ; potato 301 

Echinochloa crusgalli 37S 

Edgerton, C. W. 271, 278, 331 

Edson, A. W. 254 

Ellis, J. B. 94 

Elymus4io; arenarius 410 ; virginicus 

244 
Empetrum nigrum 195 
Empusa Muscae 77 
Engler, A. 94 
Entomophthorales 136 
Entomosporium 290 ; maculatum 365 
Entyloma 372, 380 ; compositarum 3S1 ; 

Physalidis 380 ; Ranunculi 381 
Environmental factors 62 
Epidemics 6 
Ergot 244 

Ericaceae 74, 209, 439, 440 
Erigeron 381 
Eriksson, J. 3, 57, 201, 221, 384, 408, 

415, 416 
Erysiphaceae 63, 77, 81, 175, 209, 215 
Erysiphe 221 ; Cichoracearum 217, 228; 

graminis 79, 80, 216, 217; Polygoni 

217, 227 
Eschenhagen, F. 75 
Essary, S. H. 328 
Euchlaena luxurians 377 



502 



GENERAL INDEX 



Euphorbia 223, 402 ; Cyparissias 398 
Eustace, H.J. 165, 295, 301 
Everhart, B. M. 94 
Exoascaceae 63, 77, 81, 175 
Exoascus 175; Cerasi 185; deformans 

176; Pruni 183 
Exobasidiaceas 439 
Exobasidiales 439 
Exobasidium 439 ; Andromedae 440 ; 

Azaleae 440 ; Oxycocci 440 ; Vaccinii 

440 
Eycleshymer, A. C. 97 

Facultative parasites 63 

Fagopyrum esculentum 297 

Fagus 173 ; grandifolia 466, 467 

Fairchild, D. G. 226, 365 

Falck, R. 370, 375 

Farlow, W. G. 3, 94, 136, 147, 152, 158, 

213, 248, 422, 427 
Farneti, R. 297 
Faurot, F. \V. 194 
Ferguson, M. C. 55, 60, 72 
Ferrouillat, P. 254 
Fertilization tube 143 
Festuca sylvatica 420 
Ficus carica 393 
Fisch, C. 244 
Fischer de Waldheim 370 
Fischer, E. 196, 209, 384 
Fission fungi 103 
Fixing solutions 41 ; chrom-acetic 43 ; 

chrom-osmo-acetic (Flemming) 44; 

mercuro-nitric 45 
Flasks, cleaning 14 
Floyd, B. F. 367 
Fly speck, apple, etc. 367 
Fomes 443, 464 ; applanatus 464, 467 ; 

fomentarius 464, 467 ; igniarius 464, 

465 ; Pinicola 464, 467 
Formalin 91 
Fragaria 139, 226, 261 
Frank, B. 3, 93, 343, 477 
Fraxinus 454, 458; americana 464 
Freeman, E. M. 93, 375, 416 
Frenching 234 
Fries, E. i 
Froehlich, H. 74 
Fruit spot, apple 341 
Fuckel, L. I 

Fulton, H. R. 297, 322, 469 
Fungi, classes of 94 ; imperfecti 285 
Fungicides 7 ; application of 87 ; prep- 
aration of 88 
Fusarium 288, 303, 320; Lini 319; Ly- 

copersici 318; oxysporum 239, 317 
Fusicladium, dendriticum 264 ; Pyrinum 

264 



Gall, cranberry 138; heaths 440 

Galloway, B. T. 4, 229, 301 

Garman, H. 107 

Gaylussacia 440 

Gelatin, nutrient 29 ; sterilization 20 

Gelidium 26 

Germination 8 ; methods 57 ; require- 
ments 55 ; studies 55 

Geyler, II. 439 

Gloeosporium 79, 205, 288, 303, 330; 
ampelophagum332 ; apocryptum335; 
cingulatum 331 ; fructigenum 331 ; 
Juglandis 335; laeticola 335; Ligus- 
trinum 335 ; nervisequum 279, 331 ; 
Ribis 205, 331 ; Tiliae 335 ; Venetum 

334 
Gloiopeltis 26 
Glomerella 254, 331 ; rufomaculans 36, 

27 1' 289, 334 
Glyceria nervata 244 
Glycerin agar 28 
Gnomonia254; leptostyla 336 ; Veneta 

278 
Gnomoniaceas 175, 254 
Gnomoniella circinata 205 
Gorham, F. T. 104 
Gossypium 121, 233, 296, 304, 313, 325, 

445, 479 ; hirsutum 449 
Grafting wax S3 
Granville tobacco wilt 134 
Grout, A. J. 301 
Guignardia 254, 290; Bidwellii 254; 

Vaccinii 259 
Gymnoconia 389, 390 ; Peckiana 427 
Gymnosporangium 80, 389, 422 ; clava- 

riasforme 426 ; globosum 426 ; macro- 
pus 425; Sabinae 426 

Halsted, B. D. 97, 158, 171, 243, 248, 
271. 317. 336, 343' 344. 345' 346, 347, 
348, 350, 403 

Hanging-drop culture 57 ; rings for 59 

Harding, H. A. 107, 131 

Harper, R. A. 52, 136, 215, 370 

Harrison, F. C. 131 

Hartig, R. 3, 93, 173, 202, 242, 2S0, 321, 

467- 473 
Hasselbring, H. 282, 332 
Heald, F. D. 244, 293 
Heart rot, beets 343 ; sugar maple 452 
Hedgcock, G. G. 114 
Hedrick, U. P. 85 
Heinz, A. 134 
Helianthus, annuus 141, i6i, 420; tu- 

berosus 161, 420 
Helminthosporium 288 ; carpophilum 

337 
Helotiaceae 175, 203 



« 



GENERAL INDEX 



503 



Hemibasidiomycetes 370 

Henning, E. 408, 415 

Hennings, P. 433 

Hepatica acutiloba 418 

Hesse 141 

Heteroecism 387 

Hieracium 422 

Hitchcock, A. S. 376 

Holway, E. W. D. 407, 417 

Hordeum 218, 377, 410 ; bulbosum 218 ; 
decipiens 218; distichum 218; hexa- 
stichum 218; intermedium 218; ju- 
batum 218; murinum 218; secalinum 
218; sylvaticum 218; vulgatum 21S; 
vulgare 410; Zeocriton 218 

Howard, A. 469 

Howell, J. K. 395 

Humphrey, J. E. 158, 187, 198, 248 

Hyacinthus orientalis 120 

Hydnaceas 442 

Hydnum443; coralloides453; erinaceus 
453 ; septentrionale 452 

Hymenomycetales 441 

Hymenomycetes 72 

Hypertrophies 5 

Hyphomycetes 49, 285 

Hypochnus 451 

Hypocreaceae 175, 232, 248 

Hypocreales 247 

Iberis umbellata 99 

Imbedding 45 

Indicators, titration 33 

Infection, artificial 8, 76 

Infiltration 45 

Insect breeding cage 82 

Introduction i 

Ipomoea Batatas 243, 344, 348, 449, 479 

Isaria 286 

Isolation 9; colony 36; cultures 9, 10, 

12, 34, 35; materials 34 ; series 36 
Istvanffi, G. de 196 

Jackson, H. S. 85 

Jacky, E. 421 

Jaczewski, A. V. 254 

Jahn, E. loi 

Jensen, J. L. 372 

Johnson, E. C. 375 

Jones, L. R. 121, 131, 165, 301 

Juglans, cinerea 331, 335, 45S; nigra 
1 14, 458 ; regia 120 

Juniperus 423 ; barbadensis 463 ; com- 
munis 426; virginiana 423, 425, 426, 
463 

Karsten, P. A. i 
Kellerman, W. A. 372, 379 



Kissling, E. 196 

Klebahn, H. 204, 208, 278, 336, 384, 

398, 415, 433 
Klebs, E. 10 
Knot, olive 1 18 
Knowles, E. L. 376 
Koch, R. 10, 16, 76 
Kriiger, F. 343 

Kiihn, J. 3, 67, 93, 399, 445' 477 
Kusano, S. 136, 421 
Kiister, E. 5 



Labiatae 407 

Lablab vulgaris 398 

Lactuca 164; sativa 196, 198, 363, 446, 

449 
Lafar, Fr. 94 

Larix decidua 202, 45S, 463, 467 
Late blight, celery 361 ; potato 165 
Lathyrus pratensis 398 
Laubert, R. 335 
Lautenschlager, sterilizer 21 
Lawrence, W. II. 264 
Leaf blight, cotton 313 ; cranberry 338 ; 

pear and quince 365 ; tomato 362 
Leaf blotch, rose 357 
Leaf curl, peach 176 
Leaf-splitting blight, sugar cane 263 
Leaf spot, alfalfa 203 ; beets 309 ; pear 

358; strawberry 261 
Ledum palustre 195 
Lee, A. B. 41 
Leersia 380 
Lepidium sativum 141 
Leptosphseria circinans 479 ; Coniothy- 

rium 356 
Leptothyrium 290 ; Pomi 367 
Lesions 5 
Leveille, J. H. i 
Lewton- Brain, L. 330 
Light, relation of fungi 68, 71 
Ligustrum vulgare 331 
Lilium 196 

Lime-sulfur wash 90, 92 
Linum 319 
Liquid media 23 
Lister, Jos. 10 
Litmus milk 25 
Lodeman, E. G. 85, 248 
Loeffler, Fr. 9 
Lolium perenne 244 
Lupinus albus 211 ; angustifolius 211 ; 

luteus 211 ; thermis 211 
Liistner, G. 147 
Lycopersicum esculentum 1 34, 300, 302, 

318, 330. 362, 449 
Lysigenous cavity 137 



504 



GENERAL INDEX 



Macchiati, L. 134 

Macrosporium 286 ; Catalpae347; Iridis 

304; nigricantium 79, 304; Sarcinula 

304; Solani 301; Tabacinum 304; 

Tomato 304 
Magnolia grandiflora 347 
Magnus, P. 140 
Malvaceae 419 
Manure decoctions 24 
Marasmius 443 ; plicatus 469 ; Sacchari 

469 
Marsonia 289, 336; Juglandis 336; 

ochroleuca 336; Populi 336 
Massee, G. 93 
Mathiola incana 99 
Mayr, H. 239 

Mc Alpine, D. 337, 384, 399, 40S, 417 
Meat extracts 25 
Media, sterilization 15 
Medicago sativa 140, 203, 328, 477,479 
Melampsora 3S9, 390 ; Larici-tremulae 

437 ; Magnusiana 437 ; Pinitorqua 

437 ; Rostrupii 438 ; tremulae 437 
Melampsoraceae 3S9 
Melanconiales 286, 28S 
Meliola Camellise 213 
Metcalf, Haven 28 1, 297 
Microsphasra 221 ; Alni 228 
Migula, W. 103 
Mildew (powdery), apple and cherry 

226; composites 228; gooseberry 

221; peach 224; grapes 229, 357; 

peas 227; willow and poplar 230; 

trees 231 ; woody plants 228 
Miles, G. F. 479 
Milk 25; sterilization 20 
Millardet, A. 3, 85, 158 
Miyabe, K. 304 
Miyake, K. 141 
Moisture, relation of fungi 66 
Mold, onion 304 
Mollisiacese 175, 203 
Monilia 186, 286 
Monoblepharidales 135 
Morphology 2 
Morse, W. J. 131 
Morus 134 
Mucedineae 286 
Mucor 23 ; mucedo 64 
Mucoraceas 49, 56 
Mucorales 135 
Miiller, J. 208 
Murrill, \V. A. 281 

Mycological advances 12 ; relations 4 
Mycology, systematic i 
Mycorhiza, endophytic 75 
Mycosphaerella 254 ; Cerasella 263 ; 

Fragarias 261, 296 ; stratiformans, 263 



Mycosphaerellaceag 175, 
Myxomycetes 95, 97 
Myxosporium 279 



:S4 



Nawaschin, S. 97, 195 

Nectria 232 ; cinnabarina 239 ; ditissima 

240, 242 ; Ipomoeas 243 
Nees von Esenbeck, C. G. i 
Neger, F. W. 215 
Nemophila auriculata 211 
Neocosmospora 232; vasinfecta S3, 233, 

320 
Nerium Oleander 118 
Neutralization, culture media ^^ 
Newcombe, F. C. 427 
Nicotiana Tabacum 134, 210, 304, 315 
Nitrogen, relation of fungi 73 
Nordhausen, M. 196 
Norton, J. B. S. 187, 376 
Nowakowski, L. 136 
Nummularia 254 ; discreta 282 
Nutrient salt solution 28 
Nutrients, relation of fungi 73 

Obligate parasites, 63 ; saprophytes 63 

O'Brien, Abigail 71 

Qidocephalum albidum 56 

CEnothera biennis 139 

Oidium 218,286,480; Tuckeri 229,286 

Olea europaea 118 

Olive, E. W. loi, 384, 394, 408 

Onobrychis Cristagalli 211 

Onygena corvina 56 

Oochytriaceas 139 

Oospora 2S6 ; scabies 290 

Orange rust, aster and golden-rod 435 ; 

blackberry and raspberry 427 
Orchidaceae 75 
Orton, W. A. 233 
Oryza sativa 247, 297, 380 
Ostrya virginiana 473 
Oudemans, C. A. J. A. 3 
Oxalis 415 
Ozonium auricomum 480 ; omnivorum 

479 

Paddock, W. 334, 350 

Palla, E. 231 

Pammel, L. H. 107, 309, 363, 395, 422, 

444. 479 
Panax quinquefolium 211, 305, 320 
Panicum 378 ; sanguinale 298 
Paraffin process 45 
Parasitism 62 
Paris green 92 
Pasteur, L. 1 1 
Pastinaca sativa 291, 312 
Pathology, practical 3 



GENERAL INDEX 



505 



Patterson, Flora W. 175 

renicillium 23, 56,71, 145; glaucum 69 

Peridermium 436 ; acicolum 436; strobi 

433 
Periplasm 143 
Perisporiaceas 175 
Perisporiales 209 
Peronospora 148 ; parasitica 161 ; Schlei- 

deniana 162; sparsa 164 
Peronosporaceas 49, 63, 72, 77, 14S 
Peronosporales 55, 136, 140, 141, 147 
Persoon, C. II. i 
Pestalozzia 289 ; Guepini 338 ; Ilartigii 

339 

Petri, L. 118 

Petri, R. J. 10 

Petunia 69 

Phacidiaceae 175, 207 

Phaseolus 119, 227; lunatus 171; vul- 
garis 397, 449 

Phleum pratense 244, 415 

Phlox 228 

Phoma 260, 2S9 ; Batatae 344 ; Betae 74, 
343; radicis74; Solani345; uvicola2 56 

Phragmidium 389, 390 ; subcorticium 

430 
Phyllachora Trifolii 298 
Phyllactinia 221 ; Corylea 231 
Phyllosticta 260, 289, 314, 345; Ampe- 

lopsidis 347 ; Catalpae347; hortorum 

346; Labruscae 256; limitata 352; 

maculicola 347 ; Paviae 345 ; Pyrina 

347,352; solitaria 346; tabifica 344 ; 

Viola; 347 
Physalis pubescens 380 
Physiological relations 5, 55 
Physiology 2 
Phytomyxaceae 97 
Phytomyxales 97 
Phytophthora63, 67, 147, 148; cactorum 

173; infestans 65, 72, 165; Phaseoli 

171 
Picea 458, 463, 467 ; excelsa 432 
Pierce, N. B. 118, 120, 176, 315 
Pink rot, apple 295 
Pinus 173, 339, 463, 467 ; cembra 434; 

rigida 436 ; strobus 433 ; sylvestris 

436 
Piricularia 287 ; grisea 297 ; Oryzae 298 
Pisum arvense 398; sativum 211, 227, 

398' 449 
Plant decoctions 23 
Plant pathology, rise of 2 ; section of 3 ; 

modern 4 
Plantaginaceas 164 
Plasmodiophora 97 ; Brassicae 97 
Plasmopara cubensis 158; Viticola 65, 

152 



Platanus occidentalis 278 

Platinum needle 35 

Plectascineas 209 

Pleospora herbarum 304 

PleosporaceiE 175, 254 

Pleurotus ostreatus 38 

Plowright, ('. B. 370, 384 

Plowrightia morbosa 248 

Plum pockets 183 

Poa2i7; compressa4io ; pratensis 247 

Podosphaera 221 ; leucotricha 224, 226; 
Oxyacanthae 226 

Polygonum 393 

Polyporaceae 442 

Polyporus 443 ; Betulinus 464 ; borealis 
463; carneus463; Fraxinophilus464; 
Juniperinus 463 ; Schweinitzii 463 ; 
squamosus 453 ; sulphureus 39, 457 

Polythrincium 287, 298 ; Trifolii 298 

Pomeae 423 

Populus 185, 230, 336, 458; alba 114; 
tremula 437 ; tremuloide« 438, 466 

Potassium sulfide 90 

Potato disease 165 

Potter, M. C. 131 

Powell, G. H. 367 

Prillieux, Ed. 3, 93, 2S0 

Pritchard, F. J. 408 

Protobasidiomycetes 384 

Protozoa 136 

Prucha 107 

Pruning 128 

Prunus 1 14, 185, 187, 226, 263, 314, 458, 
471; americana 249,339,417; Amyg- 
dalus 1 16, 315, 417 ; Armeniaca 116, 
188, 249, 299, 335, 417; avium 185, 
249, 473; Cerasus 185, 249; domes- 
tica 183,417,473; pennsylvanica 249-, 
Persica 114, 176, 187, 224, 335, 336, 
417 ; serotina 249,417 ; virginiana 249 

Pseudomonas 106; campestris 67, 105, 
107; Hyacinth! 106, iii, 120; Jug- 
landis 106, 120; malvacearum 106, 
120; Oleas 106, 118; Phaseoli 106, 
119; Pruni 106; radicicola 73 ; Stew- 
artii 106, iii, 120; Syringae 107; 
tumefaciens 114; vascularum 106, 
120 

Pseudopeziza 203, 331 ; Medicaginis 
203 ; Trifolii 204 

Puccinia 389, 390; Asparagi 403; Chrys- 
anthemi42i; coronata42o; dispersa 
416; fusca 422 ; glumarum4i6; gra- 
minis 80, 408 ; Flelianthi 420 ; Hiera- 
cii 422; malvacearum 419; Menthae 
407 ; Peckiana 430 ; Phlei-pratensis 
415; Pruni-spinosae 417; purpurea 
414; I'ubigo-vera 416; Sorghi 414; 



5o6 



GENERAL INDEX 



suaveolens42i ; Tanaceti42o; Trag- 

opogi 421 ; Violse 407 
Pucciniaceae 3S9 
Pueraria 137 
Pure cultures, establishing 37 ; methods 

9 

Puriewitsch, K. 74 

Pycnochytrium 138; aureum 139; glo- 
bosum 139; Myosotidis 139 

Pyrenomycetes 174 

Pyrus 114, 123, 185,423; Aucuparia 195, 
426; communis 1 16, 123,264,358, 365, 
426,458; coronarja 425 ; Malus 123, 
226, 239, 242, 264, 271, 341, 346, 347, 
350, 367,425, 426, 458, 471 

Pythiaceae 140 

Pythiacystis 141, 148; Citrophthora 144 

Pythium 78, 141, 148, 151, 446; de 
Baryanum 141, 157, 173 

Quaintance, A. L. 187 

Quercus 185, 280, 454, 458, 466, 471 ; 

alba 278, 473 ; coccinea 278 ; velu- 

tina 278 

Radicula Nasturtium-aquaticum 141, 

149 
Ramularia 287, 296; areola 296; rufo- 

maculans 297 ; Tulasnei 262, 296 
Ranunculaceae 381 
Raphanus sativus 99, 149, 162, 449 
Rathay, E. 175 
Reddick, D. 254 
Reed, G. M. 215, 217 
Reed, H. S. 320 
Resin wash 215 
Resistant varieties 85 
Rhizoctonia 78, 210, 444, 478; Betae 

445; Medicaginis 446, 477 
Rhizopus nigricans 71, 349 
Rhododendron hirsutum 196, 432 ; fer- 

ruginium 196, 432 
Rhytisma Acerinum 208 ; Salicinum 

209 ; Vaccinii 209 
Ribes 204, 221, 240, 363, 364, 393, 433 ; 

aureum 435; irriguum 435; nigrum 

435 ; rubrum 435 
Richards, II. M. 384, 422, 427, 440 
Robinia Pseudo-Acacia 458 
Robinson, B. L. 175 
Roestelia Pyrata 425 
Rolfs, F. M. 444 
Rolfs, P. H. 327 
Root disease, sugar cane 469 
Root rot, alfalfa, cotton, etc. 479 ; fruit 

trees 471 ; tobacco 210; vine 321 
Root and stem rot fungus 444 
Rprer, J. B. 346, 352 



Rosa 114, 164, 224, 357, 430 

Rosaceas 114, 139 

Rosellinia 254 ; Quercina 280 

Rostowzew, S. J. 147 

Rubus 114, 139, 334, 354, 363, 427 

Rumex 402 

Russell, H. L. 107 

Rust, apple 425 ; beans 397 ; carnation 
399 ; clover 395 ; currant 423 ; fungi 
384; hollyhock4i9; maize 414; mint 
407 ; poplar 437 ; rhododendron and 
Norway spruce 432 ; roses 430 ; stone 
fruits 417; timothy 415; vetch and 
garden pea 398 ; violet 407 

Rytz, W. 136 

Saccardo, P. A. i, 94 

Saccharum officinarum 120, 263, 330, 
469 

Sadebeck, R. 175 

Saida, K. 74 

Salix 114, 209, 230, 454, 458 

Salmon, D. E. 244 

Salmon, E. S. 79, 215, 221, 22S, 231 

Sands, M. C. 215 

Sanitary environment 7 

Sappin-Trouffy 393 

Saprolegniaceae 49 

Saprolegniales 136 

Saprophytism 62 

Savastano, L. 118 

Scab, apple 264 ; peach and apricot 299; 
pear 264 ; potato 290 

Scald, cranberry 259 

Schizomycetes 95, 103 

Schrenk, H. von 114, 271, 457, 463, 464 

Schroeter, J. 3, 94, 136, 147, 175 

Schweinitz, L. D. i 

Sclerospora 148, 161; graminicola 161 ; 
macrospora 161 

Sclerotinia 185, 186; Aucuparise 186, 
195; baccarum 186,195; Betulas 186, 
201; cinerea 187; fructigena 186, 
187, 286; Fuckeliana 186, 196; het- 
eroica 186, 195; Libertiana 186, 198, 
201 ; megalospora 186, 195 ; Oxy- 
cocci 186, 195; Rhododendri 186, 
196; Trifoliorum 186, 201 ; tuberosa 
186, 201 ; Vaccinii 186, 195 

Scolecotrichum 287 

Scott, W. M. 85, 194, 271, 346, 352 

Scribner, F. L. 4, 152, 254, 261, 278, 

313- 332, 334- 347> 357. 365- 417 
Secale, 217 ; cereale 217, 244, 383, 410, 

416 
Seed selection 86 

Seedling stem blight, egg plant 345 
Selby, A. D. 114, 176, 367, 381 



GENERAL INDEX 



507 



Sempervivum 173 

Senecio 164, 435; elegans 210 

Separation cultures 34 

Septogloeum 289 

Septoria 290 ; Chrysanthemi 364 ; con- 

similis 363 ; Dianthi 363 ; Lycopersici 

362; Petroselini 312, 361; Pyricola 

3 58 ; Ribis 363 ; Rubi 363 
Setaria 161 ; crus-ardeas 247 
Seymour, A. B. 94 
Shear, C. L. 138, 259, 338, 440, 479 
Shot-hole disease, plum and cherry 339 
Sicyos angulatus 159 
Siliciate jelly 28, 31 
Sinapis 99 

Sirrine, F. A. 165, 301, 381, 403 
Sisymbrium officinale 99 
Slides, cleaning 14 
Slime molds 97 
Smith, C. O. 118 
Smith, Erw. F. 9, 103, 104, 107, iii, 

114, iiS, 119, 120, 121, 129, 134, 1S7, 

224, 233,317 
Smith, Grant 215 
Smith, R. E. 67, 120, 144, 196, 198, 264, 

336, 403 
Smith, Theobald 18 
Smith, W. G. 93 
Smut, blue-stem grass 378 ; corn 5, 

376; oats 372 ; onion 381 ; wheat 375 
Sodium silicate 31 
Soft rot, calla 133 ; carrot 131 
Solanaceae, wilt 134 
Solanum, Commersonii 16S; Melon- 

gena 134, 345, 346; polyadenium 

168; tuberosum 134, 165, 290, 301, 

444> 449 
Solid media 26 
Solidago 402, 435 
Solutions, relation of fungi 75 
Sonchus 164 

Sooty blotch, apple, etc. 367 
Sooty mold, orange 213 
Sooty spot, clover 298 
Sorauer, P. 3, 93, 187, 366, 444 
Sorbus 283 
Sorghum 377, 414 

Sorosporium 371 ; Syntherismse 378 
Southworth, E. A. 278, 325 
Spallanzani 1 1 
Spaulding, Perley 271, 434 
Sphaerella Gossypina 313 
Sphaeriaceae 254 
Sphaeriales 253 
Sphaeronema fimbriatum 348 
Sphasropsidales 286 
Sphaeropsis 290, 347 ; cinerea 353 ; Mali 

353; Malorum 350, 353 



Sphasrotheca 221 ; Ilumuli 226; Mors- 
uvas 221 ; pannosa 224; phytoptophila 
81 

Spieckermann, A. 131 

Spinacia oleracea 164 

Spirillum 103 

Spongy dry rot, apple 316 

Spontaneous generation 1 1 

Spores, heat resistance 17 

Sporonema 279 

Sporotrichum 286; globuliferum 71; 
Poae 293 

Spraying 7 

Stager, R. 244 

Staining 48 ; filamentous fungi 48 ; 
fleshy fungi 49 

Stains, carbol fuchsin 49, 53 ; Congo 
red 50; Ehrlich-Biondi-Heidenhain 
50; Flemming triple 51; gentian 
violet 51 ; iodine green 53 ; iron 
haematoxylin 52 ; Loeffler's methy- 
lene blue 53 ; Magdala red 50 ; 
Mayer's paracarmin 50; nigrosin 51; 
orange G 50, 51 ; saffranin 50, 51 

Starch jelly 29 

Steam sterilizer 16; pressure 19 

Stem rot, clover 201 ; sweet potato and 
egg plant 243 

Stereum 443 

Sterilization, at 100° C. 16; hot air 21 ; 
principles 1 1 ; principles and methods 
15; soil 21 ; under pressure 19 

Stevens, F. L. 316 

Stewart, F. C. 107, in, 158, 165, 204, 

293. 3°'' 329. 354' 381, 399. 433 
Stigmatea Mespili 366 
Stilbeae 303 
Stock cultures 2i7 
Stone, G. E. 67, 198, 403 
Stoneman, Bertha 271, 331 
Stuart, Wm. 165, 372, 376, 399 
Sturgis, W. C. 171, 290, 301, 312, 321, 

367- 381 
Subcultures 37 
Sulfur 90 

Swingle, D. B. 317 
Swingle, W. T. 85, 147, 372, 375, 379 
Sydow, P. 384 
Synchytriaceas 136 
Synchytrium 137, 138; decipiens 138, 

139; fulgens 139 
Synthetic liquid media 25 
Syringa 228 

Tavel, F. von 95 

Technique 10, 41 ; fixing 41 ; imbedding 

45; staining 41; histological 8 
Tecoma radicans 315 



5o8 



GENERAL INDEX 



Temperature, high 70; low 71; opti- 
mum 69 ; relation of fungi 69 

Ternetz, Charlotte 74 - 

Test tubes, cleaning 13 

Thaxter, R. 162, 171, 210, 290, 3S1, 422 

Thelephoraceae 442 

Thielavia basicola 210, 348 

Thuya occidentalis 463 

Tilia 454 ; Ulmifolia 335 

Tilletia 372; foetens 379, 380; horrida 
380 ; Tritici 380 

Tilletiaceas 371 

Titration, culture media 33 ; Fuller's 
procedure 34 

Tolyposporium 371 ; bullatum 378 

Tourney, J. W. 1 14 

Townsend, C. O. 114, 133 

Trabut, L. 337 

Tragopogon 421 ; porrifolius 152, 421 

Trametes 443 ; Pini 467 

Transfers 37 

Tranzschel, W. 427 

Traverse, G. B. 161 

Trelease, W. 162 

Trifolium 141, 201, 204, 298, 328, 479; 
carolinianum 396; hybridum 395 ; in- 
carnatum 395 ; pratense 298, 395 ; 
repens 395 

Trigonella coerulea 211 

Triticum 375, 379, 410, 416 

Tsuga canadensis 458, 468 

Tubercle 1 18 

Tuberculariae 28S 

Tubeuf, K. von 93, 196, 201, 433 

Tulasne, L. R. and C. i, 95, 244, 370, 

445' 477 
Tyndall 17 

Ulmus, 185, 454; americana 283 

Uncinula 221 ; Aceris 231 ; necator 
229 ; Salicis 230 

Underwood, L. M. 95 

Unger, F. 93 

Uredinales 55, 63, 77, 80, 81, 384 ; 
families and genera 388 ; synopsis 
of species 391 

Urocystis 372 ; Cepulse 87, 38 1 ; oc- 
culta 383 

Uromyces 389 ; appendiculatus 397 ; 
Betae 399; Caryophyllinus 399; Pisi 
398 ; Rumicis 402 ; Solidaginis 402 ; 
scutellatus 402 ; Trifolii 395 

Urophlyctis 140; Alfalfse 140; lepro- 
ides 140; pulposa 140 

Uschinsky's solution 26 

Ustilaginaceae 371 

Ustilaginales 63, 77, 370 

Ustilaginoidea Oxyzae 247 



Ustilago 371; Avense 372; levis 373; 
Reiliana 377 ; Tritici 375; Zeae 376, 

Vaccinium arboreum 209 ; macrocar- 

pon 259, 338, 440; Myrtillus 195; 

Oxycoccus 139, 195; uliginosum 195; 

Vitis-idaea 195, 440 
Valsaceas 254 
Van Hall, C. J. J. 103, 131 
Van Tieghem cell 57 
Vegetable products 29 
Venturia 254, 287; Pomi 264; Pyrina264 
Verbena 227 

Vessels, sterilization of 15 
Viala, P. 152, 229, 254, 321, 332 
Vicia 227 ; cracca 398 
Vigna marginata 398 
Viola 139,308, 315, 347,407; odorata2io 
Vitis 114, 152, 229, 254, 274, 314, 321, 

332; aestivalis 154; cordifolia 154; 

Labruscse 1 54 ; vinifera 1 54 
Volutella 288, 332 ; Dianthi 317 ; fructi 

316 

Wager, H. 50, 149 

Waite, M. B. 122 

Wakker, J. H. 120, 125, 186, 469 

Ward, H. M. 71, 93, 141, 165, 197, 381, 

408, 416 
Water fungi 135 
Water molds 140 
Water-pore infections 108 
Webber, H. J. 213 
Wehmer, C. 187, 239 
Whetzel, H. H. 119, 122, 162, 305,322, 

397 
Whipple, O. B. 224 
White rot, deciduous tress 453 
White " rust," crucifers 149 
Wiesner, J. 69 
Wilcox, E. M. 471 
Wilson, G. W. 147 
Wilt, cucurbits 129; cotton, etc. 233; 

flax 319; Solanaceas 134 ; sweet corn 

II I 
Winter, G. 3, 94 
Witches' broom 5 ; cherry 185 
Wither tip, citrus fruits 327 
Woronin, M. 3, 97, 187, 195, 439 

Xanthium 393 
Xylariaceae 254 

Zalewski, A. 149 
Zantedeschia asthiopica 133 
Zea mays 1 1 1, 141, 161, 376, 414 
Zimmermann, A. 41 
Zopf, W. 95, 136, 210 



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